The UFC has 1 women's division, at 135 lbs. It makes no sense to have the champ in non-title fights when there's 1 weight division.
Cyborg can get pissy about Rousey all she wants. Yes Cyborg was dominant before Rousey showed up. But she blew it when she got busted for Steroids, and had to go away for a while. Plus, she had a tendancy to make 135ers come up to 145 to face her.
Dolce is convinced he can safely get Santos to 135.
There's no reason for Rousey to move up. If you want the champ, you come to the champ.