Why do white people borrow culture from others?

I'm going through this debate with my girlfriend. why do white people, especially youth seem to borrow from other cultures. For example- Rap music and baggy pants- The origination of both of these is from black culture. I just see so many white guys trying to dance [with pants down to their ankles] in a style that doesn't come naturally. Or Fergie, Justin timberlake, etc borrowing constantly. Sound one way on record, and when interviewed, they're from harvard. My girlfriend thinks it's a cl issue [not culture/race issue]. I think White people in our country don't have a strong, defined culture anymore [except for the good ol' boys].