Huh? In the United States books have inflated by -0.1% per year since 1997, compared with the overall economy which inflated at 2.46% per year on average during the same period. Because of the stiff competition.

Unless you mean specifically textbooks, which are inflating because piracy has destroyed the demand (the annual revenue of the textbook market is down ~33% since 2014, despite increases in both prices and enrollment in colleges). You can see the causal link here as increases in pricing are lagging decreasing sales. If the prices were driving the decreasing sales you would expect the opposite behavior.

Why start at 2014?

https://archive.attn.com/stories/1164/heres-exactly-why-coll...

Between 1975 and 2014 college books outpaced inflation over three times.

You should look at that chart a bit more carefully.