I think it's more a matter of investment vs. payoff. I read TLotR from beginning to end once and I liked it, but it's such a time sink for so little payoff that I wouldn't do it again. There's so much else I could do with that time instead. I'd rather put the movies in the background while I do something else over the course of nine hours, or maybe reread a specific bit I liked. It's not about instant gratification, it's that we're no longer constrained in our media selection. 70 years ago you might have reread the books right after finishing them because you had nothing else to do. That's not true today.