First, Kanji signs are more detailed than the alphabet and uneven lines can make it really ugly/hard to read. Same issue with breaking lead, causes ugliness.
Second, traditionally handwriting in Japan have been seen as a way to measure one's upbringing; you can fake looks and style but if your handwriting is bad, that signals that your parents didn't raise you well. This was(and still is in some places) the reason resumes have to be handwritten.
So tools that helps your handwriting had uses beyond just utility.
(my handwriting is garbage and I'm happy IT and tech jobs doesn't check this)