Why are blitz players so good?

My rapid rating is 1700 and my bullet rating is about 1550. My blitz rating, however, has never surpassed 1250. Recently, I got humiliated by a 1200 rated blitz player who crushed me three games in a row. Why are the blitz players on chess.com seemingly so good, and why is it so difficult to gain rating past 1200?

i have no clue i am stuck at 1248 actually i'm not stuck i just don't like blitz

blitz is good moves fast. I play fast, but not necessarily good. Blitz players generally have ideas integrated in their heads much better than rapid players, but also more shallowly. 

Being good at blitz is mostly just about memorising patterns and trusting your intuition.

Your first 10 moves of the opening you pretty much premove, except to make sure your opponent doesn't take a weird sideline or try to do something dirty like LeFong you.

In the middlegame, you spend 15 seconds coming up with a quick strategy "I'll prepare an f4 pawn break and attack on the kingside" and then when the position gets sharp and you have a potential sacrifice, you just trust your intuition if it looks promising "if I sac a knight on f7, my opponent's king looks fairly exposed, let's just go for it and see what happens."

In an endgame, you're usually too low on time to do any real calculations, except to make sure you have the opposition and do a quick square count to make sure you don't lose a pawn race.

Blitz generally encourages bad habits like not calculating stuff deeply and relying too much on your intuition and biases. You can train yourself to be good at blitz, but it might come at the cost of hindering your growth in slower time controls.

You essentially shut down your brain to learning new ideas and just keep doing the same thing you currently do, but faster.

Blitz and bullet ratings are both tougher at the lower levels, after 1850 it starts to even out again. This is most likely due to newer players mostly playing rapid as they start with Chess, as they should.  chessgoals.com/rating-comparison/

I suggest a different rating to more accurately reflect how good you are: https://www.chess.com/forum/view/site-feedback/suggestion-different-stats-59883752

Using Komodo10 as a basis, your blitz should be around 150 above your rapid, and your bullet should be about 300 above your rapid. This is because blitz and bullet ratings are inflated compared to rapid. Assuming you play at the same strength in rapid, blitz, and bullet, your ratings should match the pattern mentioned (rapid=rapid, blitz=rapid+150, bullet=rapid+300). Of course, this isn't true for most people due to how well/bad they perform under time trouble.

Do you also suggest we don't subscribe to gravity anymore so that we can fly?

The op didn't ask for your opinion on how blitz chess could improve your chess skill. he asked why the blitz players are so strong. I tried to come up with an answer. You did not.

Why are blitz players so good? because they're not bad

This is a valid question.

There are so many blitz players - most actually - on this site at the lower levels (I can't learn to play this game worth a damn so I'm stuck there, so I know) - who have never played rapid, or daily, or whatever a "normal" time control would be (weird that the two choices are "rapid" and "daily" and nothing in between, no?) and play at a level where you can't make a single blunder, or they will instantly and surely (and in less than 5 or so seconds) jump on it.  

It doesn't seem statistically plausible, but maybe I'm mistaken and there are just millions (yes literally millions, given  my sampling and chess.com's "new member" numbers...) of middle-tier club level players that just have no interest in puzzles or normal time control games, playing blitz at literally every hour of every day here, that could just go and reliably  insta-wreck 80% of  everyone in their local club, but don't, because, COVID or something, I guess?

I'm doing some rigorous statistical analysis of this situation.    It's interesting.   Will publish soon.

Oh, and they all mostly play the same 5 or 6 very uncommon (and "unsound at master level") openings.   Next level!!!!!   (How many times have y'all seen the busch-gass gambit at your local park, mmmm?)