People didn’t have much in the way of alternatives before the typewriter was invented. There was a great emphasis on having clear, legible handwriting.
People either wrote by hand or not at all. So there was a lot of emphasis on having good handwriting in letters and documents and people just got better at through sheer amount of practice they were getting.
Now since the advent of keyboards no one cares about handwriting anymore and it has been antiquated outside of signatures. Keyboards do the same thing perfectly every time with less effort.