Being nice isn't compliance or neediness unless you feel bitter or jaded about doing it. No matter what some people may think, relationships aren't a zero-sum game. If you feel like you're giving more than you get, then you're either chasing the wrong person or you are the wrong person to be acting the way you are. If you're really happy together with someone, doing nice things for them should come without thought or any preconceived notions of what you'll be "getting back." If things are really right, you'll feel even better every time you make their life a little more pleasant. If you're not happy, and still putting out all that effort, just get the fuck out of that relationship as soon as you can into something more fulfilling. Why waste your time in an ongoing situation that brings you no joy?
Why do we treat them so well? We treat them so well because they're our friends. In some cases our best friends in the world.