I confess; I have always had appalling handwriting. Even in the Sixth Form teachers were making me write in print or with a pencil to try and improve my writing. One of my boyfriends went to Uganda for a year (before Idi Amin). He said he loved getting letters from me; they took weeks to fully decipher and occupied many an empty hour!!
I wasn't careless about writing, I tried really hard to improve it, but to no avail. In my 40s I was diagnosed as dyspraxic, with very poor fine motor skills, which finally explained the problems I had.
Oddly enough I do do quite a lot of writing, of the notes and lists variety, plus at meetings and further education classes, but the notes/minutes will be typed up within two days of the meeting, while I can remember enough of the meeting to decipher my notes.
But from time I was able to purchase the luxury of a manual typewriter I have typewritten anything that was intended to communicate with other people. I will handwrite notelets to thank people for whatever, but for personal letters, I type the body of the text but handwrite the greeting a the top and the sign off at the end.