I would say it was growth that killed it, and what would kill any platform that allows some sort of public-facing, user content.

Keep adding people, and you would both lower your bar towards an obviously low average, and you increase the pressure to "particpate", which is damaging even to scenes that do have high barriers of entry [1].

MS added the KPI-maxxing corpo cancer that boosted the decay, but I don't believe they were a cause. To quote the AI bros, "it's inevitable."

[1] https://en.wikipedia.org/wiki/Publish_or_perish