1) Usually my rapid is higher than blitz and this is higher than bullet. This is the common trend because longer time controls give more time to think and hopefully translates to higher playing accuracy and this means higher ratings.
Ratings naturally fluctuate a lot though, so it is possible that some rating categories will overtake others. There are also people who focus on blitz or bullet only, so their rapid rating is really low for them. Of course, they could probably gain rapid rating if they wanted to, but this is just an example of how rapid isn't highest for everyone always.
2) It depends what rating range we are talking about. Under 2000 chess.com rapid rating, the people who don't play rapid is usually because they don't want to; they like faster time controls for fun, but this isn't necessarily helpful for their long-term chess improvement. They probably SHOULD be playing rapid more. I guess the short answer of why many don't play rapid much is because many people don't want to invest the time into improving as much as having fun. Some people claim 10 min chess is too long and they don't have the time for it, but that same person will play speed chess for an hour -_-
Over 2000 rating, I'm still an advocate for rapid chess, but now people may begin fazing out of rapid in favor for blitz chess because it is more difficult to get paired with an opponent as one gets really high. I'm 2000-ish range rapid and I don't have this problem yet, but I know from 2000s above my rating that they say there are longer waits for getting a 10 min chess game accepted at the higher levels. That is why many switch over to blitz.
Imagine a top Grandmaster like Hikaru Nakamura (@Hikaru), if they wanted a rated rapid game, they basically have to wait for another top player around their level to also be looking for a rated rapid game to be paired. There aren't too many people in the world as good as him, so he may have a while to wait! This happens to a lesser extent around 2000 range, but probably around 2200-2400 rating (or higher) this wait becomes more noticeable.
Lastly, I just wanted to mention that 10 min chess (rapid) is still statistically the most popular time control on chess.com, so most people do play rapid; this applies for "good players" as well. Most "good players" also play rapid. Your forum thread is probably asking why they don't play it even more than they do, so this is what I answered.
I hope my responses helped. See you around chess.com 
can anyone answer these 2 questions?
1)is ur rapid rating always higher than ur blitz and blitz higher than bullet?
2)how come most good players dont play rapid?