It died because running a communication platform for humans on the internet is hard. In particular it died because whatever moderation it had (almost none TBH)

It died because running a communication platform for humans on the internet is hard. In particular it died because whatever moderation it had (almost none TBH) was no barrier to bad actors, so it drowned in spam and troll posts. Then the centralized social platforms took over with their network effects and moderation paid for from ads.