I think the reason for this is simply because
most of the listeners come from the suburbs, and they listen to music as some form as escapism. They want to hear stories from a foreign environment, something interesting that they're not hip to. So suburban affairs aren't going to be as interesting of a story to tell compared to hood affairs, because a lot of drama comes from that. Which would you rather hear, the story of how someone grew up in a harsh environment and had to push through all odds to succeed? Or, the story of someone who had an average life, living in an average house, going to an average school and sleeping with their average girlfriend.. and somewhere along the way, they wanted to rap?
Now, granted... Just because you come from a neighborhood that was relatively peaceful, doesn't mean you don't have issues that people can relate to. And that also doesn't mean you don't go through issues either. Everyone does. For a hood rapper, it's easier to find inspiration. All he has to do is go outside or look out his window. The suburban rapper can't do that. But in a way, this is more of a blessing than a curse, because this forces him to be creative and he's got a lot more to prove. It doesn't matter who you are, if you're self-aware of the world, you can write about topics that can touch anybody. Whether you're hood OR suburban. Tupac was active but he reached everyone, because not every song of his was "Ambitionz Az A Ridah" or "To Live and Die in LA". He had Changes, Brenda's Got A Baby, Dear Momma and many more. So if anything, it's the hood rapper that's at a disadvantage, because he's in a box. There's only so many things he can write about. The suburban rapper has more opportunities to see the world, and therefore, has a much wider range of topics he can touch on. Look at J. Cole. He's in the Top Three and didn't move a single Ki.