You don't get better at what you don't do.

English books use different registers, vocabulary, and grammatical tenses than found in everyday speech also. Basically every language has differences in formally printed books and daily speech.

And it's not like you have to read dense texts only. There are plenty of short books, or books with lighter material, that learners can definitely read. It's a very good way to discover new vocabulary and see how words are used in what contexts.