[Reki]

Every medium has creation and consumption costs, and it affects their average quality. Books have a high creation cost: both in time and money, relative to electronic mediums. They also have a high consumption cost, as you cant read a book in a few seconds like you can watch shortform content. These factors select for quality.

[zemvpferreira]

You could say the same for TV or film and most of it is still garbage.

[Reki]

True, but their cost is still relatively cheaper considering the profit you can make from them is more than from books. Part of this is also because they are easier to replicate.