I think for one, people had mixed feelings on GOTG 2, and it seemed that she didn't leave a mark there. If you look at a lot of reviews, they never mention her, and some reviews even said she was a pointless character.
There's even a Top 50 MCU character list and she's #50. Hell, I think a lot of people think she's worthless cause she doesn't fight
But then again, Infinity War is a movie everyone is seeing, and she's actually doing cute stuff there, so I think her fan base is growing. Hell, just yesterday, Pom was one of the most searched actors on IMDB behind Brie Larson and Josh Brolin.