Because even my absolute favorite mouse* only has six buttons, while my keyboard has well over a hundred, and the amount of information I can convey by combining them is far greater than what I can express with a few buttons and crude relative spatial positioning.
Because I work with tools where using the keyboard shortcuts until they become reflex is an option, rather than only occasionally using programs and hoping they're "intuitive" enough to use by looking for what I want to do and pointing at it.
Because using language is more expressive than pointing at things all day.
Because you can't refer to something by name with a mouse unless it's already on a menu. (Well, mouse gestures could be considered an attempt to do this, but the set of "letters" is very limited.)
When a task is primarily spatial (typically, graphical editing; I'm not a gamer), I use the mouse. That's about it.
Because I work with tools where using the keyboard shortcuts until they become reflex is an option, rather than only occasionally using programs and hoping they're "intuitive" enough to use by looking for what I want to do and pointing at it.
Because using language is more expressive than pointing at things all day.
Because you can't refer to something by name with a mouse unless it's already on a menu. (Well, mouse gestures could be considered an attempt to do this, but the set of "letters" is very limited.)
When a task is primarily spatial (typically, graphical editing; I'm not a gamer), I use the mouse. That's about it.
* http://www.amazon.com/Kensington-Expert-Optical-Trackball-64...