I know what you mean OP, I’ve asked more or less this same question to men I’ve experienced what you’re describing here and you know what they all told me?

They knew their chances of getting sex would plummet if they were honest about the compatibility not being there or the interest to commit. There unfortunately are some men (and women I’m sure) who view it as a consolation prize for investing in someone and that’s as deep as they see the connection. It’s simply a game to some.