I think camping is more of an issue with the map design than the game. If there's only one entrance to the base, people are going to guard it. It's the most effective way to prevent enemies from grabbing the flag. With a well laid out map containing multiple attack paths, sitting in one spot suddenly becomes very ineffective.
Although, in a way, there is something that keeps people from sitting still for a really long time: the idle timer. Sit still over a minute and you get booted to observer.