I believe the problem with children-oriented sites and communities were that the spaces provided a false sense of security for children and parents which led to at least the social spaces being prime targets for predators.

While these communities would have strict moderation as well, I think there were some cases where some community moderators were abusing their position which can happen in any social spaces, but children’s spaces are held to a much higher level of scrutiny for obvious reasons.

Then there’s the issue of scaling and regulations. As Internet usage continued to explode, it would’ve become much harder to scale up the amount of mods needed, which becomes much more expensive when it’s a full time job. Then I believe a good number of large/influential countries also moved in on regulating how companies maintain data for child accounts and I think restricting targeted advertising for children specifically, which would have made it much harder for companies to make money while also dealing with increasing expenses in moderation and hosting upkeep.

It doesnt explain everything completely, but I think that’s why these places disappeared