Well, a lot of the Black writers whom you're thinking of are intentional provocateurs, and they've built up their own "echo chambers" over the course of many years (which is why their followers number in the thousands). I suspect they keep churning out new iterations of the same "one-trick pony" content because it's the same loyal base of followers who keep reading their work. I'm not so sure Medium is even intentionally curating them as often as they did during past years -- in fact, one of them recently came out and complained about how her Medium readership was down, and, for that reason, she was going to write/publish on her own independent blog a lot more frequently than posting article on Medium.

But then again, Medium only has a limited reach. It's a matter of reaching people beyond this platform, as well.