If you got two girls at home ready to have sex at the snap of your fingers, why would you travel cross country to see a girl who may or may not sleep with you?
If a girl resists after the several times, you don't ask her what's up, you decide if it's worth to keep pushing to close the deal. Sometimes they just want to know how desperate you are, how many options you have, how smooth you are. It's all a game.
Personally I wouldn't say anything, unless she directly puts you down, I would just keep on seeing her less and less and hit on other girls. Make yourself more valuable to the opposite sex. She'll wake up soon.
To ask a girl "why wont you have sex with me?" is like asking a customer "why won't you buy this car?" Pretty desperate.