Good question! I was surprised she was hated when I started engaging with fandom.
I like her, but she is the straight man in this show, most of the time she isn’t even a character, just the voice of reason, I kinda assume that’s part of it. I do think she has a character though, but when she does develop characterflaws, that is so contrary to her role as voice of reason, even if it fits her character, that it become a bit hard to understand her.
Also sexism. Less here on reddit thankfully, hardly any in this sub actually, but I’ve seen the Skyler logic applied to her in other places
Everytime Diane tries to solve her own problem someone else shows up and she has to solve their problem too because she thinks that’s what it takes to truly solve her own problem even if she could’ve just left it alone or ordered a cab all along.
She’s also stuck in a place, fancy Hollywoo party, where she doesn’t belong and doesn’t even want to be but leaving is too complicated.
Also, other people being idiots ends up being in her way and keeps her from doing her own thing.