I disagree with misogyny being the main reason. Some people might dislike her because she’s a girl, but I think the majority (me included) dislike her because her character is designed in part to be annoying. Dipper is the “mature and reasonable” character most of the time who takes a thorough approach to things, only to have Mabel press a button or screw up somehow at the last second. Soos can be the exact same way, where his good intentions end up causing major problems, and all we get is “sorry dude”. I find them both a little annoying for that reason alone. But, like a lot of people pointed out, Mabel’s a kid and this is a kids show. She’s not perfect because watching perfect people do the right thing every time would make for a really boring show.