why do so many people hate their inlaws?

 I know I can't stand mine. But why is that? Is there some scientific reason that we are programmed to not like these people? Other people like them, why can't I? I just can't. And, to think they raised the man I love so deeply. How did they even do that, being opposite of what I love? 
I'm serious right now. I would like to know if there is something biological about not liking inlaws. Or if it's just that some people really get unlucky with who their inlaws are.