I mean, it's not just programming books. Books and magazines for a lot of specialist fields are on the way out, since the internet is just a more convenient option.

Look at video game or pop culture coverage for example. With a few specialist exceptions, no-ones reading print media for info on them anymore. Things like YouTube and social media and specialist websites are just a lot more practical and up to date.

I get that books make it easier to go slowly (or for writers to spend the time researching), but tech is just a fast moving field. By the time something is available in print form, it's probably already near irrelevant for work purposes.