Why do Masters not play rapid

Obviously this is very general, but I'm curious as to why masters almost only play blitz and bullet (Hikaru, Éric Rosen and Naroditsky to name a couple) even though they do actually play classical/rapid (Hikaru at candidates). Wouldn't it be better to train yourself at rapid or classical instead of playing blitz and bullet where it is more important to play fast?

Stalling and cheating make long games unplayable for high ratings. I'd guess the current glass ceiling is around 2300-2400... which is much better than it used to be, so chess.com's cheat detection is probably better (well, they also refund rating). Years ago the ceiling was closer to 2000.

Also, like you said, they play OTB classical tournaments, which is their serious chess. Online is for fun... and speed games are a lot of fun.

One of my theories is 10 minutes is an awkward time control for strong players who have sped up their calculation process enough that 3+0 is slow enough to play satisfactory moves, and if the benefit of calculation is logarithmic, the next natural time control up may be something like 30+0, IDK.

Grandmasters like Daniel Naroditsky often play rapid games on stream for instructional purposes, and they frequently run into cheaters. I think that is definitely a factor.

As for 1 minute bullet or faster: as mentioned above, it's fun and there's more adrenalin involved. Also, there's almost no time for calculation, so strong players depend largely on their experience and highly developed pattern recognition and intuition. (With calculation I mean selecting candidate moves and calculating long lines and evaluate the results, not seeing a mate in 3.) To some extent it becomes a test of intuitive chess understanding. Of course this does not apply to noobs like myself, where it's more about not blundering enough to get mated before the opponent runs out of time... 

Good players hate to lose.
Without cameras etc the good players prefer 1|0 bullet to avoid possible cheating.

Check out this guy match list and you'll understand why.

@moem1958

Even around my rating it's getting hard to find decent opponents to play time controls 15+10 or longer. If you're around 2400 then you have no opponents to play with.

And a few weeks ago some dumb baby was arguing with me about reporting anyone you lose to when you're a high rated rapid player... can't remember the username.

we all hate to lose