Why is the caps lock key often so big on a keyboard?

It seems that the caps lock key is not a frequently used key on a computer keyboard yet on all the keyboards I have used, it is afforded a significant amount of interface real estate, often as much as the backspace space key and more than quite a few other keys such as delete, arrow keys and escape.

The caps lock key is used in some specialist applications: engineers use it, as do people with poor motor control of their hands and I imagine graphic designers who often use capitals for stylistic reasons also benefit from it's existence, but even in these cases it will be still be an infrequently used key.

Why is it so big? Should it be resized or put in a different position on the keyboard?