If you're getting what you want out of your reading then more power to you, but I think you'll find that devoting your full attention to what you're doing fundamentally differs from doing it in the background. Why play GTA when you could just listen and enjoy the book? What is GTA adding to that experience?

I think a lot of people, including, I presume, most who willingly choose to study literature, enjoy reading as an activity unto itself and so don't feel the need to add additional distractions. Not everybody finds sitting down and "ploughing through" (how disdainful a phrase!) a book unappealing.