I think that MC doesn't ask about her family because "family" isn't that big in his life. His whole family is him and Neil. Either Neil is an only child with no living parents (at least that I recall) or Neil is estranged from them, and of course his mother's family has nothing to do with him. He didn't spend time with siblings or cousins doing fun stuff, he had a lonely life with few or no real friends up until he met Zoey who also came from a messed-up family. Note how he reacts to Maya's camping story, it's a foreign concept to him. He doesn't have the frame of reference that makes him think that other people's families are something to talk about, especially when talking about his is so uncomfortable. The first time he gets asked about his mom by the girls he pulls out his patented "yeah, too bad she's dead" bombshell which shuts down any more family talk from them. The only time he talks to any of the other girls about their families later is when they bring it up.