Why wouldn't people read programming books outside of university classes? How do you improve your craft? Reading is an instrumental part in growing as a developer and as a human being.
You're talking about whether people should. I'm talking about whether people actually do. As for why people wouldn't read, there's one giant reason: people don't care about programming.
Obviously you care, and I care, and arguably most people reading HN care. But I believe that for a large percentage of programmers, programming is just their job. They do it, they get paid for it, and as long as they can keep getting paid for it, they don't need or care to "grow as a developer". It's just not a priority in their life, or even a goal.
