For me it's a few things. For starters, she's overrated. I'm not saying she doesn't have talent - she has a good voice, is a good performer, has some good songs. But I don't overly enjoy any of those things about her. Everyone treats her like a God but to me she's just a "good" pop star - nothing revolutionary. Imo she doesn't deserve ALL the praise and awards she gets.
I also really don't like that she "borrows" heavily from other artists. She uses a ton of samples, straight up copies a lot of performances, etc. She seems really shady when it comes to that.
Imo she should be on more of Katy Perry's level of popularity and not Madonna's (back in her prime). She's not legendary to me so I just don't get that.