...gonna play some Devil's Advocate here...
i'm sure it's 'cultural', just as with the music here that we identify with. Let's say, for example, that you ('you' meaning anyone out there, not 'you' specifically), as a fan of industrial music, decide one day that you want to share your philosophical genius with the whole world and 'tell it like it is'. You have something to say and whether it's religio-socio-polital or conversely, just plain fun, you need to spit it out lyrically, electronically and musically.
What do you do?
Start a MoTown quartet? Watch Nascar, learn about trailer-life (i live in one so i can make fun. Besides, these people are damn entertaining) and mew about it with a twang? Get a Mega-Corp backing and spend most hours of your existence being shaped and molded to impress the masses and garner income? Coffee houses as an indie-artist?
No. Methinks you would go with the genre you love and know and identify with. THAT does not invalidate anything you would have to say or offer. It's your chosen medium. Of course you would express yourself that way. Some stray and some fuse. And that is how new things happen =)
But most humans express their ideas in frames of familiarity; past experience being especially of dominant import. So if you grow up in a very certain and specified culture, it's very natural to want to express yourself via that.
The fact that you (now i actually mean 'you' NEU) 'cannot' understand is curious to me. i get that most people that listen to 'our' genre of sounds really HATE rap. i, for the most part, agree. It's a very different culture. But really, is the message so different? Again, not advocating or illuminating, but the good stuff voices change. And being self-aware, as a human cognizant of the shite that occurs all around us, each of us chooses our own medium in which to speak our thoughts/concerns.
But yes, Gansta is positively fuktarded. The poets that are trapped in that choose their own device. They have become fuktards and no respect in mine eyes. At least here where i live, i can say 'No' versus 'go'
Moral of the Story?
Don't believe the HYPE