Why in most rap videos I see more butts than human faces?

Maybe that's what fans of that type of "music" (or whatever it is) are most interested in?
It's a market, it's business, they live from clicks. Butts will get them clicks, so they put as many butts as possible on display. If shoulders led to more clicks then they'd show shoulders.

Cause you are listening to slut ass shit

What year is this?

'Cause faces don't twerk

Does it matter?

your troll persona is so inconsistent, this post is crotchety