Why are Americans so uncared?

I'm a college student and in our college there's a distinct difference between american students and international students. you can tell the difference immieadiatly. It's a private university (but both internationals and americans pay the same amount). for example, in a normal school day, every single international student that is from south america, europe or middle east dresses up like they're out of a fashion magazine. this goes both for boys and girls. boys with their shiny jeans, tshirts and shirts, girls with their shiny bags and clothes and shoes. american on the other hand go to cl with sweatpants, sweatshirts that have the college's name on it.. girls are uncared, no makeup, horrible nails. i don't know, what do you think is the reason for this?