Here the human condition can flourish in a more localized way, with more participation (less lurking). No more winner takes all.
Digg to Reddit was a unique case, because Digg very specifically fucked up their site, badly, with the V4 update. Reddit was in a great spot to pick up users from Digg because of not only having a similar overarching purpose as a link aggregator, but additional features like subreddits which enabled more smaller and casual link sharing and comment sections. It was a clear upgrade from Digg V4. I do think that Reddit would have eventually overtaken Digg anyway, and V4 only sped up the process.
Technically and product-wise, there's not a whole lot wrong with Twitter right now. If you're on there to look at funny memes, cat pictures, celebrity news and pornography -- which encapsulates about 98% of Twitter use cases -- it still functions much better than the alternatives. The migrations are happening for meta reasons, either political or ToS-related (specifically, X claiming they can use images you post for AI training). This isn't a recipe for long-term success, it's a precursor for people making bunch of noise for a month and then heading back to Twitter.
As someone who doesn't really participate in these large social networks -- even modern HN is way too mainstream for me honestly -- I do think it's a good thing people get off them, though. Smaller communities are a good thing. Shouting your loudest, hottest political takes on Twitter so you can pat yourself on the back for 10k likes is a fast track to mental health issues.
The Bluesky app both performs better and uses much less battery than Twitter does. I think because it uses Google ads now, but not sure.
Twitter also has disk space leaks - I regularly find the app has gone up to 3GB or so. (And it's not from image caching, seems to be an SQLite db of all accounts I've seen posts from.)