Comment by WillAdams

Possibly because things such as:

https://mathcs.clarku.edu/~djoyce/java/elements/elements.htm...

didn't get grandfathered in, but more likely because teachers just search for:

https://www.google.com/search?q=handwriting+worksheets

and grab the first free result.

That said, I would recommend:

https://www.handwritingrepair.info/

and

https://sites.google.com/view/briem/free-books