A variety of reasons:
Opportunity: If you want some fake shit, ask people their opinion about how they would behave and they give a fake idealistic answer. If you want the real answer, give them some power and watch the results. Ronda was given attention, money, and power and she acted like a spoiled bully. That's a strike.
TUF: Tate baited her good, but Ronda just misbehaved. Then she blamed "editing" just like how BJ Penn did it. No, there were definite sequences where they pointed the camera at her and let it roll for thirty seconds, no cuts. She acted like a moron, unedited.
Hype: Kinda not her fault. But no one likes Orwellian bullshit where stuff is shoved down our throats. Ring magazine cover and "best ever" dribble from Rogan. But look at the gifs and you clearly tell she has terrible technique. This gulf between fact and fiction probably caused the biggest damage.
Sore winner, suicidal loser: Just bad attitude all around. WTF is up with her behavior. Cray cray Ellen interview where she cried about offing herself like her father, and immediately laughing because she wants to have Travis' babies. Just seconds between crying and laughing. Seriously, you have no idea how frightening that is to most men. Imagine having to sleep next to that and trust nothing metal will be slipped in-between your ribs during the night. Trusting that with your children, your finances, your well-being. Remember that she's boasted about piecing up her boyfriend who tried to get back with her. Imagine getting freed up by a woman with some domestic violence beef only to have her boast about it in the future like it wasn't a crime.
This is coming from a fan who enjoyed all the fights from Strikeforce, including Gina, Cyborg, Coenen, Tate, and some Invicta fights. I loved watching Ronda fight in Strikeforce and the UFC, and the Tate rivalry was nice to watch. I think the hype train caught up with her, and she became insufferable.