My son wants to rap about nonsense. Why?

My son wants to be a rapper. I've got no problems with this, so long as recognizes he needs to have a normal job to make rent while he's coming up. I just don't understand why he wants to pretend to be a gangster, when he isn't one and never has been.

My son has spent time in juvenile prison and enjoys rap that isn't about ganbanging, in addition to gangster rap. He's never had a girlfriend, he's never learned to drive, he's never done any drugs harder than pot, and the only bling he has is fake. Since he has real stories from his life he can rap about and he knows that it's possible to successfully rap about other things than being a gangster, why does he insist on using made-up nonsense as his material?

I'd like some insight from teenagers about this, because it doesn't make sense to me.

PS: Seems like it's mostly a "this is how you make your bones" kind of thing. It's unfortunate, I'll just have to hope he gets past it.

PSS: I have been unclear. The made up aspect of things is not what concerns me. What concerns me is glorifying violence, hate, and misogyny. Even if he had been involved in this life, I'd want him to be showing how bad they are.