Good find for sure, I was wondering if the sound localization was very bad or limited, but I'm glad this is just a bug. I was confused more than once trying to track footsteps only to realize I was wrong. Otherwise agreed it should be audible enough, but certainly should be masked by gunfire or any realistically louder noise.
In fact, the fact that it is audible prompts attackers to walk instead, which makes it harder to rush in and surprise, as it should.
Also not sure what's wrong with camping when defending, that's the whole point. I'm a big CoD4 player and I despise camping. In TDM. Because it's cheap and easy and not necessary at all for that game mode. In objective-based modes however, it's not only expected but kind of necessary to defend points. I have no reason to complain against it, and all reasons to do it.
Bottom line: in a "do anything you can to win" situation, such as is in objective-based game modes, competitive or casual (all insurgency game modes), you should expect cautious tactics and attempt to counter them. At least I found complaining about it is useless. And it only feels logical to do honestly. You attempt to win or you don't.