There's 3 reasons why a lot of people turned on Roman, none of which were Roman's fault and only two that I agree with (which are bookings fault).
First, he wasn't Daniel Bryan. People need to get over that shyt. That's stupid and always was. I can see complaining about part timers and shyt, that sorta makes sense but complaining about Roman just because he wasn't Daniel Bryan was dumb.
The second reason is the McMahon tailor made

push. Fans turned on Hogan for that push. It took longer back then but they eventually did. It's not interesting booking. Cena got turned on within a year with that same push.
Note: Austin and Rock never received the

push and actually made more money for WWE than anyone.
Lastly, they changed Roman's character. This is also something they did with Cena. People liked the throwback jersey wearing white rapper gimmick. He had an edge with that character. Once he became The Marine character people started to turn on it. Then he became fruity pebbles and the rest is history. I always respect Cena for his promo and ring work but they fukked up on his character, he could have been a bigger star than he became.
With Roman they had him telling shytty jokes, it's nonsense. It's trash. It's catering to 5-year olds who are only a small minority of the fans.