Like Mastodon? https://mastodon.social/about

How is this different from twitter aside from decentralized part?

Open source and open standards are the other big draws. Otherwise it does seem to be closely based on twitter style interaction.

You mean Diaspora - I think it's clear by now why this concept can't work.

I haven't really followed up on diaspora much, but why is that?

Isn't the idea behind diaspora something similar to sub-reddit's/facebook groups? You find a "pod" of interest/relation and join up. Thus a focus on the social/community aspects.