I've always wanted to say something very direct when an acquaintance or a client asked why I read so much, but I used to be a bit too cautious to verbalize my real beliefs out loud. But if a prominent, knowledgeable person supports my beliefs publicly, I'll happily repeat them. I have, however, gotten to the place over the past ten years when someone asks why I read the NYTimes, The Economist, a cutting-edge book like the brilliant work of retired Supreme Court Justice Stephen Breyer(subtitled "Why I Chose Pragmatism Not Textualism" [originalism]) or any top magazine or journal, I can be fairly direct. It usually comes out like, "look, there's no way you can become intelligently aware of what's going on in this world unless you read the Times or the New Yorker and The Economist." That's true whether or not you agree with the writer.
But here's General Mattis verbalizing my actual beliefs in the context of the military: If you haven't read hundreds of books, you are functionally illiterate and you will be incompetent because your personal experiences alone aren't broad enough to sustain sustain you. Any commander who claims he is "too busy to read" is going to fill body bags with his troops as he learns the hard way.