Lots of programmers that I've met always says that "He is not a UI guy." The fact is that development nowadays, whether web, Windows, Linux, OSX, or any other type of development now comprises software with a good-looking UI.  Why do so many developers seem to not like UI work?
I'm not a UI person either. Well, I do UI on my own projects, but at work I have nothing to do with it -- my work is in the guts of the app, not on the front end. 

Beyond that, I think it's more boredom than hate. Designing the UI is the hard and challenging part. Implementation is mostly grunt work. There's very little challenge or innovation in how one can implement a user interface, and there's only so many times one can put a checkbox on the screen before going slightly mental. And that's not even touching on spending hours aligning pixels "just so".
