There's also no reason why one wishing to cross the United States could not spend 4 to 5 days driving rather than 4 to 5 hours flying. Convenience is likely the primary motivator for choosing the latter in both examples, no?
If all other current word processing tools were available without the convenience that a printer offers, I imagine people would be doing exactly that.
One could still choose to type up something they've drafted on a computer, of course, just as one could still load up a car and drive half the day for several days while spending the other half in diners and cheap motels.