So I agree that Dreamwidth is great in terms of who runs it and where the money comes from, but 'lack of a mobile client' (and how it's in my experience effectively unreadable on mobile devices) is a huge when (IIRC) at least 90% of Twitter use is on mobile.

I don't think people are saying 'help, I need a social network, any social network, to keep in touch with these specific people I am in a community with' - it's that Twitter does specific things that mean people use it a lot, and make connections with new people in certain ways, and there isn't currently a smooth way to do those things without Twitter.