Why hasn't Vince done anything? Well the angel has all along been that some power higher up is holding their hand over Nexus, and the RAW-GM has been giving them easy breaks all along. I dont know if Creative has it all planned out, or if they play by ear, but, story-wise they have relatively free reigns. They're obvious goal was to A) get contracts they felt they deserved B) Win titles. Now I can think of several possible backers who would like to see the established stars culled and humiliated. Take your pick.
And what WWE accomplishes is to make the fans familiar to fresh wrestlers, some of whom may have many years at the top level ahead of them. Others will without doubt end as jobbers or be future endeavoured.
Win-win. And Barrett has what it takes to hang with the big boys, both in-ring and on the mic.