This is an interesting point so I looked it up and yeah, depending on the year, the percentages are really high!
āThe percentage of books adapted for film vary each year, sometimes substantially, as trends in popular culture must be followed. For example, in 2005 66% of films released were based on books, this then dropped significantly to 28% in 2011 and then rose to 65% in 2015.ā (From https://medium.com/publishing-in-the-digital-age/book-to-film-adaptations-caec7c65e96a )
That doesnāt mean theyāre all good though š