I have a simple answer. Fidelity of control, especially when it comes to aiming, or games that have a lot of keybinds. Controllers just don’t have enough of either of those, especially when being fast is required.
WoW is a perfect example, there is just no way I could ever play a game like that with a controller, there are just too many different things to have to do. Console games, because of the inherit control scheme, tend to be a bit more simplistic in nature. That’s not really a dig, I like a lot of console games, and have owned a console since they sold pong at Sears. Consoles can be really great, and can be more relaxing. I used to have a 52" plasma hooked up to my xbox in my bedroom. Few things can match the joy of lying in bed playing Xbox on that thing.
At the end of the day, they each have their strengths, I like them both for that reason.