MLP: FIM caught all of the autists at once, and that meant all of the creative output of that auitism was concentrated into one fandom.
I think many of those autists moved to vtubers, but that creative output is spread across all different oshis and corpos. People are still making videos and video games and fanfics and art and mods, but it's spread across many hundreds of different vtubers and we just ignore stuff outside of our fandoms, so that output doesn't appear to be as much as it previously did.