WWE obviously could not sustain Becky's character, that was clear from the day it started. It's legit a miracle they were able to keep interest up in Becky/Ronda from Survivor Series to WM, and I think 90% of it was due to social media shenanigans because on screen they came about as close as possible to ruining the whole thing. Becky's whole character and motivation stops working once she achieved all the things that motivated her. All the things she had to talk about before are gone: She's on all the posters, she had all the titles, she main evented WM, she's the focus of TV even to the point of making her boyfriend (who was also champion) play second fiddle and look like a nerd. She has nothing left to complain about WWE holding her back, and that was the main aspect of her character that caught on in the first place. In fact it's just the opposite: Now they're over pushing her.
This is a problem every single time a character is centered around the company not pushing them enough. The only time it worked and was sustainable was with Austin, and in that case it was a once in a life time break out star and they also booked him usually in ONE segment per Raw, and he wasn't wrestling on TV weekly. For most of 1998-1999, he would wrestle on Raw every other week if not every 2-3 weeks. He didn't become a weekly performer until after he came back from the second neck surgery in 2000. Even then, he rarely would wrestle on Raw and Smackdown on the same week. He also didn't have to keep talking about it or tell you he was the best, because he beat the shyt out of anyone in his way instead. His character motivation changed after he reached the top, Becky's has not and will not. She's just going to be told to go out there and say "Oi, I'm The Man can ya believe it, blokes" until no one gives a shyt and it's been run into the ground. Which is already dangerously close to happening already.
It's not really her fault, WWE was always going to run it into the ground and ruin it, but it also happens in MMA/Boxing as well.