men are traditionally the 'hunters' (oh how I hate using that term), who enjoy the 'thrill of the chase' and are therefore put off by women who cut them off before they can engage in that ritual. (Edit to add I'm not advocating these views, just relating that many if not most in our society still seem to subscribe to them.)
I definitely agree with you though about the idiotic idea that some men think they 'pay' for sex in various ways, but that's not limited to paying for dates. That applies to anything at all they do for a woman they're interested in. It seems that, going by that type of 'logic', the only reason men do anything for women they're interested in is in order to buy sex.
But you're right that some people do think that after a few dates a man is 'owed' sex, and that IMO is the best reason for women to avoid that by paying their own way. I go a step further in my personal life and didn't normally even want to be picked up for dates, at least at first. It's just smart thinking IMO to have your own way home in case things don't turn out well.