I don't understand why would anyone find underscores ugly. Underscores are basically spaces. And we use spaces in our language to separate words. May be text editors should draw underscores with more subtle way?
Now-dashes-are-ugly.
Now-dashes-are-ugly.
Underscores_make_full_highlighting_easy
Dashes-make-single-highlighting-easy
It's also a use case thing. Double click on each sentence and note the behavior. It depends on which one you want. We use snake case in our urls because you can copy something from the documentation and easily highlight a portion to change.