I don't think that there is a lack of reading material in the Watchtower its just that most of what they have written is a bunch of crap. Even the Watchtower knows that most of their publications are a bunch of crap. Why else would they only want you to read their latest works? Which are soon to be outdated pieces of crap not even fit for JWs to read. There were many great works of literature that came out of the 19th and 20th century but not even one came from the Watchtower Society.
In the congregations I went to reading outside of WT publications was frowned upon. Being unread was consider somewhat of a triumph. Most of the JWs I knew never read anything if it wasn't printed by the WT except maybe a newspaper. You never heard a converstation at the back of the KH about so and so latest book.