I can solve this riddle for you TS, but first they definitely have promoted here. T-Mobile commercials, Rogan pumped her up, they've ran hype train promo stuff for her. So I disagree with the premise to begin with, even if it wasn't Ronda level. But:
1. She can barely speak english. People pretend like she can fluently speak it, no she can't lol. She got better but she's still not some fluent, smooth talker.
2. She is boring. In the cage? Amazing, exciting. Outside the cage? Relatively boring. No shit talk, no crazy antics, no promotion really at all from her end. No "character". Her character is being a mom now, a lesbian couple mom. Maybe that excites some woke people, but I don't think many super woke people watch MMA therefore what's the "hook" and appeal?
3. Not "classical" attractive. Not hot. This is me being polite. She's a butch lesbian, that's what she is. Not offense, I like her as a fighter but she's quite literally a masculine side woman. Some people can find her attractive, that's fine, but most don't. There's a reason why PVZ and even Ronda who is also more masculine but still more feminine than Nunes and did have some sexual vibes to her (jeans pic, nude photoshoot, likes men lol).
Those would be the main 3 reasons. I don't mean to offend in any of them, and those are all simply truths. It's like asking, why do they promote Colby Covington, Jorge Masvidal, and Nate Diaz (zero real titles combined, one interim) MORE than Jan Blachowicz or Petr Yan?
I wonder. Again, same reasons: 1. can't speak english; 2. Boring personality wise, humble, respectful mainly; 3. well...lol won't speak on this one.