It was a skill drilled into every grammar school student and was demanded of every properly raised lady and gentleman. Now it has declined into something of a nuisance for students more apt to sketch block letters on paper rather than the slanted, flowing letters.
Cursive writing is a specialized skill.
A flowing word art form. It helps people develop their own personal style of writing. Without penmanship, your signature is a bunch of blocky letters. With it, you've added a bit of pizzazz to your name. Yes, some of the grammar rules are silly.