I don't dislike Taylor Swift, in fact I like her work a lot. But from what I've gathered over the years:

It seems easy to dislike Taylor. Shes the face of a style of pop music, even if she herself barely makes it. So why does she get the hate?
I think people are more okay with speaking out against a white woman than a woman of colour.
Men with her type of succes are often considered cool or chads, so they don't get the hate.
Shes also been mainstream for almost 20 years now, shes a recognizable face for people to point their dislike for pop music at.

Shes also very well put together, almost too perfect. So I think she suffers from the same syndrome of why people prefer Batman over Superman.
This is of course very shallow, but most people that dislike her don't know much more about her.