Because that is where Carmack posted his thoughts, not anywhere else. Original source.
Wether you like it or not, X/Twitter is still a primary posting ground for many key people in our industry.
because X is a dumb name
Yeah but it's a lot easier to turn an x.com link into an xcancel link so you can actually read it logged out .
Unfortunately xcancel has annoying bot protection these days so for individual tweets x.com is actually more usable IMO. Not that xcancel is the only remaining working nitter instance but I'm not aware of others that both work and keep their bot checks reasonable for non-Chrome users.