I have a feeling this post is some sort of joke, but as a serious comment, I think decentralization would work better if there were some way to automate assigning new users to instances. This part of onboarding is something that people I know (who have looked at Mastodon then turned down the idea of joining it) have cited as an annoyance. And I know I personally spent some time researching different instances in order to pick my instance, personally.
Contrast Revolt, a relatively recent (in contrast to Matrix) Discord alternative, which a few people people I know jumped right on – despite Discord not having any major/recent “sins” other than messing with the usernames. I mentioned that I’m surprised people so readily picked this up, and someone pointed out that there’s just one centralized place to make a Revolt account.