While Ronda had talked about going back to 145 after gaining the 135 belt, Cyborg getting popped at the start of 2012 ended all that. Call it petty (which it is), call it ducking (which it isnt), call it whatever you want, but after Cyborg got suspended and failed her appeal (where her people used Rousey's name and possible fight to try to get it reduced), Rousey clearly said that Cyborg was a cheat who fights undersized women.
This has been Rousey's position since mid-2012 and she hasnt changed that stance. When everyone moved to UFC, Rousey said she would fight Cyborg at 135 or 140, but only with strict OOC testing (which the UFC hadnt gotten up to speed at that point) to which Cyborg's reply was to leave the UFC and go to Invicta and for over 4 years tease the idea that she'll make 135 (my fav was the Dallas "I can make 135 in a week no problem") and fight.
Blame either one of them if you want, there is enough blame to go around, but since 2012 Cyborg has used Rousey's name to get recognition WAY MORE than Rousey has brought up Cyborg. Its almost like Concrete Whale bringing up Rousey every day to get more 'likes' from the Rousey haters. Good tactic for the hustle, but people get sick of the trolling after a very short time. Cyborg has reached the point of straight up trolling, especially this spring when she made 139 then afterwards said she'd only fight Rousey or Tate at 140, and then ignored Invicta wanting her to fight at the end of July while simultaneously saying no one wants to fight her.