There are several reasons why it could be considered "wrong". Moral, religious, etc. But I will say that when you do that, you devalue yourself. It says that you don't think you're worth anything but money and sexual favors, and that's all you have to bring to the table. YOU teach others how to treat you. If you teach them to treat you like trash, they will.
To a lot of people it doesn't make sense at all to spend all of your emotional, mental, and physical energy on someone you're only with for material comfort. When people weigh the cost of working for themselves vs. trading luxury items for sexual favors, most people chose to work for themselves and have the freedom to choose a partner based on mutual attraction.
I would also like to add that not all or even most, I'd wager, of the male population is fixated on looks alone when they look at the girls they want to date. When they look at the girls they would f*** or pay money to sleep with them, sure. But looks are only the first part of a man's analysis in deciding who he wants to date.