It's not enough to invent (and patent) something. You also need to document it in various ways - so people know the invented thing exists, what it's for, how to use it, how to fix it, etc.

> poor people couldn't afford to buy a whole lot of books. And neither did they write them.

Thus the rise of circulating libraries in the 18th century, and the public (lending) library system in the 19th century. Especially after the establishment of mandatory education for children.