Comment by vegabook

Because moving a pointer around and clicking on stuff is essentially quite a low-dimensional interaction. There are a bunch of things on screen and each is either clicked or not (okay, maybe hovered), at a fairly slow pace. The typical 87-key keyboard meanwhile gives you 87 on/offs right there and a good typist can be doing dozens of these per minute. Compare the speed with which a good vim user manipulates a document, with how you have to do it in Word. Of course, a graphical interface provides a much higher dimensional output device, but as an input medium with only a pointer, it's way behind the power of a well thought out command grammar.