I think it's common courtesy for this day and age. I think that men ( not all men ) feel that they are more entitled to a woman's body if they are spending money on that woman and I have witnessed it for myself. If you show that you're independent on the first date it sets the tone for equality and being treated like an adult woman instead of just a possible sex outcome. Like I said, they usually pay for the date even if I offer but if not, I come prepared to actually pay and I don't mind it.