It has to be emphasized again that women are creatures of emotion. If you are someone who thinks logically and expects anyone you're dealing with to think logically, or in other words, have a logical REASON for what they are doing, then you're going to be asking yourself, "Why in the world did she do that?" over and over?
With women, the main emotion that causes them to 'magically disappear' is boredom. The other one is when she starts feeling disgust for you when you allow her to disrespect you or you start operating outside of a masculine framework. Men typically think logically and most operate on something that resembles principle, such as if you treat me well, I'll treat you well. If you look out for me this time, I'll look out for you the next time. With women, no such thing exists. When dealing with men, women don't care how much you 'do for them'. They care how you make them feel. When you understand that, a lot of questions about why a woman is acting the way she does will disappear. "I was there for her whenever she needed, I paid for her school, I watched her kids, I fulfilled her every request. How could she do that to me?" Simple, it's not what you do for a woman, it's how you make her feel. Also, the more you do for her, the more you start making her feel like you are lesser in her mind. Just like if your boss handles your every request, you will feel like he's not the boss anymore, but you are the boss.
That's why the women you 'do stuff for' are the ones that do you bad, but the ones you are cold towards and are not really feeling are all over you. You retain a sense of mystery, challenge, etc., in her mind, thus sparking an emotion in her. It's sort of like the difference between watching a movie you've never seen before and watching a movie you like, but seeing it for the 14th time in the row. You'd much rather watch the new movie in most cases.