In short, they are fiscally conservative and socially liberal. These two things are like oil and water, they just don’t mix.
What is it to be socially liberal? Have you really ever thought about that? Some years ago it was illegal for a man to commit sodomy. In most cases it is not now. Is that change "socially liberal?" Does the conservative want to send such people to jail? I am a Christian, and I think it is sinful for people to reject Christ. Should I fight for a government that would make everyone be Christian? If I don't am I "socially liberal?"
I am quite conservative socially, and I am a libertarian. I just don't think the government should use force to make everyone agree with me. I also don't think the government should be able to use force to make me agree with everyone else. Is that "socially liberal?" If people want to be Scientologists, fine. Let them. If they wan't to fool others into joining; fine, let them. Caveat emptor. People have rights, and government should defend those rights and not violate them either. I just don't see how that is either liberal or conservative socially speaking.
Politicized social conservatives are to morality what politicized socialist liberals are to economics. In both cases, they can't be bothered to get off their butts and do the required work. (In the former case, the required work is leadership and conversion via persuasion and example; in the latter case, the required work is earning the desired standard of living via voluntary transactions.) Instead, they want the guvmint to do it for them. It doesn't work.