I don't think you've been to very many forums for games. People are far more likely to post threads if they're unhappy about something than if they're content, it's just human nature. This is why it feels like there's a lot of complaining going on.

Also, one of the main goals of a business is to make money, and they make this money by keeping their player-base interested over a long period of time. Without some kind of pacing, people tend to go through content too quickly and end up getting bored or burned out and end up quitting.