It was designed to slow people down. Otherwise, back in the days of manual typewriters, people would type so fast, the keys would hit each other and get stuck. If you make the little fingers do a lot of extra work, you can slow people down and keep the typewriters working.
Of course, it’s not a problem any more, but everyone has been trained on the QWERTY keyboard, and changing would be difficult. Kind of like switching from miles to kilometers, only worse.