Whenever I come across a new lemmy instance, it most likely has some sort of obscure TLD (.world, .ml, .ee, .me, .social just to name a few). Why aren't there more with more common TLDs?
There's a few reasons, as well as the ones listed:
.ml is a Mali domain which was being given away, so a lot of people snatched one up. This is now coming back to bite them on the ass as Mali want them all back.
Some are run by the same team, like the .world ones who have lemmy, mastodon and I think calckey. I don't think the same goes for all of them (but it may do - the .world ones are just the most high profile examples), .social just makes sense for a Fediverse social media instance.