more like celebs pretending to like playing D&D to get easy money and attention is very mainstream now
You may not be intending to, but you are seriously gatekeeping here. Ridiculously so.
Playing D&D to get easy money and attention? It's not going to help their career that much, regardless of their current level of celebrity.
The most simple and reasonable explanation is this: Most of these folks discovered D&D at some point in their lives and fell in love just like all of us here did. For some, it was in their childhood. For others, it's been recent. At the risk of going all People Magazine . . . celebs, they're just like us!
I'm sure there are a few of these D&D playing celebs who's first exposure is the celeb D&D game. So? If you're geeky, even if somewhat famous, and somebody invites you to play a fun game with a bunch of really fun and creative people, pay you, and let you participate in a rising phenomenon . . . why would you not jump right on that?!?!
One of the best things about D&D is the fans, famous and not-famous. The passion, the creativity, and (sometimes) the inclusiveness and welcoming. One of the worst things about D&D sometimes . . . is the fans, the gatekeeping fans who are resentful of sharing their hobby with a new, growing, and diverse audience.