Howard Wainer in American Scientist:
Many answers have been proposed to the riddle that the Mad Hatter posed to Alice at their famous tea party (for example, because Poe wrote on both). Let me argue for yet another one: the power of convention.
As I compose this essay, the writing desk I am using is a spanking new Macintosh laptop with many gigabytes of storage and enormous computing power. Its screen is a marvel of full-color clarity; it has a built-in video camera and microphone, and hence allows multiple methods of input and output. Yet it has a QWERTY keyboard. Why QWERTY?
The QWERTY keyboard, named for the order of the keys on the left side of the first row of letter keys, was invented in 1873 by Christopher Sholes, a Milwaukee newspaper editor. Its purpose was to split up keys that were commonly hit serially so that a too-fast typist would not jam the associated type bars. In addition to its primary goal of slowing things down, it also aided left-handed English language typists, for far more words can be typed with only the keys under the left hand than under the right.
Now, since its purpose has been long anachronistic, why do we still persist in using it? The reason is, of course, the power of convention. After it became the conventional keyboard layout and touch typists learned it, they were loath to give it up and learn a different system, even if the newer system was demonstrably superior. And so now, almost 150 years later, QWERTY has survived; and, because virtually all subsequent generations learn to type using it, the likelihood of its being improved remains small.