There's a reason for that, and it has nothing to do with "rape".
If you place yourself in a position where your affections have to be bought, then when the man has paid for them, he assumes he will get something in return. YOU are the one who helped frame this dynamic. If you didn't want this kind of arrangement, you should have gone dutch and paid for some dates yourself. That would be the egalitarian way to handle the development of a relationship of equal partners. If you're letting him pay all the time, it is NOT a relationship between equal partners. The person not paying is in a subservient position. They are allowing themselves to be "bought", voluntarily. If you find that offensive, stop playing into it in the first place and make the relationship an exchange between equals, and start springing for the check.
You can't have it both ways. If you set yourself up as a product to be bought/won, when the man has bought you/won you, he's going to expect his prize. And nobody's putting you in that position but
you, these days.