For multicellularity to emerge, Earth had to have oxygen and it took billions of years for bacteria to create enough oxygen. They were quite visionary and did it with providential perseverance.
Multicellularity first emerged 2.1 billion years ago, but something "went wrong" and it extinguished. Then, 600 million years ago, it reemerged just before Cambric explosion only 60 million years later, in which all fila (except one) emerged.