I think you're overlooking the extra layer of tension from Maya considering herself a lesbian. That she is considering doing this stuff with MC - who she clearly cares about and is the first guy she's ever been attracted to - despite, uh, being in direct conflict with her own sexual identity, is a significantly bigger choice than just 'mess around with a guy to get into the sorority'. The early dirty scenes with Maya make it pretty clear she has some significant mixed feelings about even being attracted to a guy in the first place.
I think what you see with Maya (and, indeed, with the MC and many other characters in this game) is an illustration of just how powerful peer pressure is in social situations with young people. Maya probably doesn't look at doing sex stuff to get into the HOTs as prostituting herself - she looks at it as being pressured to do what everyone else is (presumably) doing, which is why warning her that Quinn is up to no good might make her more likely to think no, everyone else ISNT doing this particular thing. And many people - men and women, especially young ones, and especially isolated and insecure young ones - will do things they DEFINITELY know they shouldn't do when receiving sufficient peer pressure. Maya's situation and personality are VERY similar to exactly the kind of person that is easy to influence in this manner: She doesn't have many friends, she feels isolated from her family, she thinks joining the sorority will save her. Quinn is going to manipulate her on exactly that basis with peer pressure, and many people - especially girls like Maya - will give in, go along, and do things they regret. For many people, that's basically the story of their social lives in late high school and early college, and that's especially true in the greek scene where hazing and peer pressure are particularly pervasive forces.
The only place here I'd disagree with you is motive. I'd agree Josy has a more openly sexual personality, but the game goes out of its way to make clear that her dad and her have made up and he's saved to pay her tuition. She doesnt NEED the money.
The game is set up to make us believe that Maya does need the money in order to stay in school. Maya has a motive that Josy doesn't and it makes all the difference.