I think most rap comes from a certain area, and if you're from an area that is blowinig up, you have a better chance of making it big. For example - LA and NYC are always gonna be big areas, followed by Oakland, Atlanta, Chicago, Miami, etc. There are all either big cities or cities with a reputation for rap music.
So until Arizona makes itself regionally known the way Atlanta did in the past 10 years, its gonna be a lot harder for an artist from AZ to make it big.
Also, LA, NYC, Chicago, New Orleans etc. are all areas with some amount of African-American culture. And I dont mean it just has alot of African Americans, but I mean that these areas have always been traditionally the breeding grounds for African-American music (Jazz, Bebop, Cool, R&B, Hip Hop, Rap, etc.).
Arizona is a relatively new area, and was not even a US state until the 1900's. I think it has a long way to go as far as forming its own identity and creating its own regional sound before it can have a lot of credibility in the rap game.