To be an alternative it had to be an alternative. Not "we had a great community with image uploads, voice chats, client parity across all platforms, miltiple servers set up in one click, songle login, game integrations etc., so now we move to this broken disjointed landscape of inconsistently implemented features"
Most users don't need every single one of those features. It reminds me of the conversations about lemmy and the fediverse after the reddit api uproar. The alternative link aggregators didn't need to do everything well, just the core things well enough to build a community that sustains engagement and becomes discoverable. But it failed at the major pieces: performance, scalability, media handling, moderation, governance, and federation. In contrast, I would argue xmpp covers a strong subset of commonly used discord features well enough to provide the chat/social component to many existing communities.