Ratings are a relative measure. They rate you relative to the pool of players.
Bullet is probably lower for the same reason rapid and daily are higher: new players prefer long time controls. Faster time controls have a comparatively stronger pool of players.
For higher ratings it seems blitz and bullet are about equal. I'm usually 2100 in both for example.
Why is almost everyone much higher rated in Blitz than in Bullet on chess.com?
Obviously some people are weaker and some stronger with quicker time controls but this should even out if looking at players in general. It seems that everyone has higher Blitz rating than Bullet rating.
It has felt like this for a long time but I just checked my last opponents profiles and of the 19 players there were two who had played only couple of Blitz games so their rating wasn't really accurate. Of the remaining 17 players only 1 had Bullet rating matching Blitz rating (only +3). But 17 last players I have played had on the average +309 higer Blitz rating than Bullet rating and no one had higher Bullet rating. Of these 17 players 5 players had over 400 points higher Blitz rating than Bullet.
Isn't the starting rating the same and isn't it supposed to follow more or less normal distribution?