How are Texas rappers able to have have music careers w/out mainstream or out of state support?

It seems like a lot of mainstream Texan rappers like Slim Thug and Chamillionaire were able to make good money and sell a lot of records even before they hit the mainstream. And then you've got people like Lil' Keke (& Z-Ro somewhat) that are able to make it with seemingly mostly in state support.