Why doesnt anyone read the rulebooks?

I am not new to RPGs I have played them for many years now. But, as I am trying more and more games and meeting more players and, trying more tables I am beginning to realize no one ever reads the rulebook. Sometimes, not even the DM. Anytime, I am starting a new game, as a GM or a player, I reserve about 2 hours of time to reading, a good chunk of the book. If I am dm'ing I am gonna read that thing cover to cover, and make reference cards. Now thats just me, you dont have to do all that. But, you should at least read the few pages of actual rules. So, I ask you, If you are about to play a new game do you read the rules? And if not, why?