And it was a bad mistake.
Internment might make sense to disrupt a domestic organisation, with a structure of cells, so there was some reason for thinking it might have worked against the IRA, but that is not the problem here. What we see are a series of ad hoc attacks using improvised weapons. The best defence against these is intelligence provided by their own community, so alienating that community through internment would be the height of stupidity.
If internment is such a good idea, why isn't it working in the USA? The gang related murder rate in US cities like Chicago is far more of a problem than terrorist violence in London, yet the USA also has the highest incarceration rate in the world.
Knee jerk solutions are more about making us feel better than addressing the problem.