I think one of the reasons most programmers don’t read books is that the constant deadline pressure of our jobs discourages taking any time during the work day and many (most?) of us work much more than 40 hours a week, so we don’t have a lot of time outside of work. However, I have always found time, somehow, to keep reading software books. I no longer read technology specific books.
As other people have mentioned, I think it is generational as well. I started programming professionally in 1979. I don’t think I had access to the internet until 1987, so my habits were established well before the web. Also, I notice that the people I know in their 20s don’t read any books of any kind not just programming books.