Like you, I read because it turns my brain off. I am able to focus reading in a way I can't doing anything else, so it quits doing 500 things at once. Also I have chronic health issues and distraction is the most effective pain killer. If I can lose myself in a book, I stop obsessing about my pain levels and can put it out of my mind as much as I can maintain a comfortable position reading. And I read to learn. I learn stuff even from light fiction in various ways.