Why do people continue to speculate about this? Cat is losing a great marketing opportunity and a title shot here. Nobody would give that up.
I don't understand the "increased marketability" point either. Is Zingano not hot enough for the fans? Tate and Zingano are like most average looking women: get the right makeup artist and they can look much hotter than they are. Sans makeup, they are average. And regardless of that, nobody has any clue how good or entertaining Rousey, Zingano or Tate will be as coaches on TUF.
To me, there's nothing fishy going on here. Zingano got hurt and the UFC was forced to go with their contingency plan: put on the only other female fans have seen and heard of. Is that a good contingency plan? Not in my opinion, but it's pretty much all they had. *shrugs*