I used ballpoint pens in school but I don't like the process: my hand often feels too tense, and getting handwriting legible is a lot of effort. Once I switched to fountain pens I enjoy the process a lot more, and the result generally look better without much effort.

I'm sure many people are OK with ballpoint pens and might even prefer the feel.

Fountain pen (+ ink and paper) doesn't really cost more than a paperlike screen protector. So it can be entirely functional. But many people also enjoy it as a hobby, collecting pens and whatnot.