Oh, hi.
Reason why is because they are human, and as humans, discourse gravitates towards topics and modes of expression people are comfortable with. Philosophy mostly, 99.99999% takes place in this mode.
Ad Homenin Attacks is hardly unusual, often codified in rhetoric as valid. What isn't valid is the prohibition against Ad Homenein assertions. A larger dialectic exists that the debates take place in. Some schools of philosophy almost exclusively reside within this intact, I recommend looking into texts like The Cynic Epistles, a text from Antiquity used (sometimes manufactured) by those advocating the Cynic style of spontaneous ad hom attacks on passerbyers stance in regards to vices and virtues, I've seen it practiced by a group in Hawaii, as part of the last remaining cell of occupied wall street (and one even wore a dog chained and howled, but knew nothing of the term Cynicism, mystery to me how that concept trickled down to me still to this day).
https://en.m.wikipedia.org/wiki/Cynic_epistles
People in general hold to this rhetorical form to lesser degrees, the talk of philosophers when in intimate contact talking with close friends won't begin to match up with how they often write, if on topics of logic. It is because philosophy in the west went through a early rhetorical split between spoken and written philosophy. You can produce far more ponderous texts solo in philosophy than you ever could in active debates as we have traditionally had them structured in the west. In India, they would debate around the corpus of the Vedas, Upanishads, and a few other texts, and the winner or losers of the debates had to support ever increasing complex questions to one another, explaining a question often in riddle form.... if they failed, they had to quit their school of philosophy and adopt the victorious school of thought. That's as advanced of a system you can produce within reason that is both scholastic yet conversational based. It avoided the issue of Ad Homs by simply forcing the defeat of your opponent and making him your think slave from then on out, they didn't have to delve into questions of if you are ethically in a place to make a assertion, cause Vedas and God trump all. The dialectic was a slave to this.
In the west we support a diversity of opinion, often imaginative, but have to structure the perceived consequences of the thought against the precariousness of the survival of a community.
I'll give you a purely satirical, imagined, extreme case:
Trixie advocates the highest good is to boil water, and leave it in a bucket positioned on top of slightly cracked doors.
I see Trixie advocate this, while setting up a bucket, and call Trixie a asshole and a moron. This is a blatant ad hom.
Others see Trixie being called a Ad Hom, says "Why you say that?"
Sister of a Suck hears this, comes rushing through a door to say no Ad Hominens, gets horribly burned, because Trixie put a bucket of scolding hot water up.
My attack was, in hindsight, a appeal to ethics. It was for the safety of person and community, a sign and signal to others in real time, in a absolutely efficient fashion, not to follow suit. Had Sister of a Suck allowed the conversation to continue, he would of heard the reason why it was such a bad idea, and wouldn't have to spend a week in a burn unit in a hospital.
Informal discussions will often evolve on this basis, sometimes the point will be understood without further digging, others are a little slow and require a longer period of time to accustom themselves to the mode of argument, and how it relates to the larger realm of complex thinking. We rarely in the west insist merely on the basis of a defeated argument you have to join the opposing view. About 50% of conversation is dedicated to this, not just in philosophy, but also in general conversation. More actually if you are a screen writer for a show like FRIENDS. This cannot be escaped save in solitary discourse, or formal written works of philosophy where all elements can be controlled like a work of art (and they are seldom read).
The art of politics often flows out of rhetorical studies, so you'll see in res publicas, be they democratic or dictorial, they often rely on Ad Homs, heavily interspersed in their speech as well as other forms of speech in attacking competing ideas. 99.9999% of legislative work involves this in western democracies.
Again, only place this doesn't work, is works of formal monkish logic. I'm Catholic, and fairly monkish, so if you want that sort of debate, hit me up, and we can set a isolated thread up and do it, but know the Protestants on this site who advocate the hardest for academic styled debates will Ad hom the loudest while we do so. It is that ingrained in their nature. Cannot be avoided.
If you are interested in this, lots of books exist on the subject. I recommend looking into the rhetoric of the philosopher Vico as a starting point, but also just meander around on google. If a topic isn't going to your liking, just bring up the idea to others you'll like to restrict the style to a particular mode of thought. Traditionally we've used "logical fallacies" to force a debate to conform to a artificial standard, but logical fallacies rarely can support themselves on their own, and can't hold off a determined opponent wanting to utterly trash a theory.
If you link your sense of self to your theories, I strongly recommend backing off from this. Ideas are thrashed and broken on a regular basis. It isn't ever going to be like in the class rooms, because that isn't real debate, given it has severe pedagogical restrictions inforced by a teacher/professor, that aims at the participation of the "common dumbest denominator", because they are paid to do so in this fashion. It is why we today have legions of morons running amok with philosophy degrees but get ripped to shreds when their beliefs are tested.
The surest way to get into debates is to observe first, figure out how other debate, then jump in. If you sit around too long without chirping in, you're in the wrong. If you assert a Ad Hom, be expected to receive one in return, or a explanation as to why. Far more challenging retorts can occur.
One of the best ad homenein discourses in the history of philosophy came from Lucian of Samosata. He was accused of "not being a real philosophy (seriously, wtf?)" or had literal professors of philosophy approach the emperor, who Lucian was closely associated with, to do him in. Back then, Emperors we moderators, except they could send you in exile, torture, or murder you. You'll see that the drive to rules are usually insidious and a pure evil, and has little basis in philosophical discourse. Lucian did the only thing a philosopher could, and made a beautiful little track where he attacked ever school of philosophy present under the most absurd and ludicrous of means, remains one of the best works of philosophical retort ever written, a true classic of philosophy:
http://www.theoi.com/Text/LucianDialoguesDead1.html
As then, so now, most trolls seek authority and righteousness, but are always incipient fools who don't know diddly squate about philosophy. It isn't found in emulation of behavior or forms of the anal retentive, or those snowflakes easily wounded, but by those ambitious enough to seek out the problems of philosophy, identify the problems we've long overlooked, and push the borders. Such philosophers next to never fit the mold society expects them to play in. They, like a great artist, can paint in many forms. If you demand your art as realist or expressionslist, they can humor you.... for a while, but that isn't the substance of their genius, their focus, who they are.
You'll find a lot of little threads where anyone will come onto this site, post a question, and receive a reply, with the response of "sorry, I was looking for a more academic discussion". I 100% want to reassure such fools, philosophy is not the field for them, be they a novice or a professor at a Ivy League school, if you demand all thought to conform to you, in only one pattern, you will not long survive in the great sea of thought we sail in. It will be nothing but chaos to you. I recommend looking into a trade like carpentry, or marble ball manufacturing instead. Philosophy is a incredible force of nature spread across many kinds of thinkers, no one thinker has the ability to see the entirety of it. We can never hope to make it uniform like a professor pretends to. Simply can't be contained. Why it can lead to exacerbation.
If you need a particular style, or a emulation of a particular thinker, ask. Someone might emulate it if they care, merely to amuse you. I strongly recommend getting rid of such a crutch and learn to broaden your horizons. You face a fierce and unconquerable frontier, don't demand others tame it for you, make it conform to your expectations.