How come UFC HW is so thin?

I mean I can only think of Randy, Nog, Frank, and Brock in the top with Randy and Nog on the way down already. GG and Kongo have huge holes that they need to work on before even dreaming of going after the title again. Junior, Cain, and Carwin still needs a year or two to stand a chance against Frank and Brock. Why can't Dana get some other guys in the UFC HW division?