Girls do it and guys do it; one day, out of the blue, they contact you as if nothing happened.
I believe that some people in a moment of reflection are truly bothered with how they treated someone, have convinced themselves that contacting them is the thing to do.
Some people do it to see if there is a chance they can slip it in one more time and there might be a few that believe people who shared a level intimacy can still be friends after the fact.
I call them all self-delusional pricks that are so wrapped up in themselves and possibly suffer conflicts of grandeur that their poor self-image cannot handle not knowing what other people think of them. Worst is someone out there thinking ill of them, with good reason, because they believe themselves to be the victim of circumstance or worse, that what they did was not their fault.