I have a suspicion that UFC 200 might be part of this.
If you want UFC 200 to be a huge event, then you need a big Rousey fight. There's only 2 really big Rousey fights right now and that's Rousey-Cyborg, and Rousey vs the #1 contender (Tate or Nunes).
Nunes has no name recognition. Tate really only has 1 more Rousey fight to lose before she's done for good.
If you put Tate in now and Tate gets clobbered, she's essentially off the table and you're left with Nunes who has no name recognition. I don't think anyone realistically believes that Holm is going to close the gap by the middle of 2016 either.
So, if you make Rousey-Holm now, you now have the winner of Tate-Nunes in your back pocket. You build the Tate-Nunes match by putting it on the Rousey card, and when UFC 200 rolls around you'll either have Rousey-Cyborg or Rousey vs the winner of Tate-Nunes.
Anyway, just thinking out loud...