I can think of one scenario only - You have a desktop app or drivers that you want to ensure will work in the upcoming non-beta, so getting a head start would be good I suppose.
But for anyone else, why would you test software for free from a trillion dollar company that have a bit of a track record now of hostility towards users.
This isn't a troll, I'm a Windows 11 user myself. I am genuinely at a loss.
Edit: I'm being a dumbass (on first coffee as I write this), there's plenty of reasons why people would download a beta... I was thinking from my perspective only!