"Why do you read what you read?"
It's a question someone asked me once, knowing that I read voraciously, knowing that my reading material ranges from the really lowbrow (Academy 7, Laurell K Hamilton, urban fantasy - I've even read Oh John Ringo No) through the ordinary rungs of genre, to more literary and intellectual of the SFF genre (Steven Brust, Elizabeth Bear, Ursula LeGuin, Samuel R Delany, Michael Chabon) with occasional forays out into mysteries, and the wild world of literature soi-disant: Angela Chambers, Anthony Burgess, Lawrence Durrell. And knowing, too, that I read widely in historical nonfiction (leaning towards the academic side) and in as much of the material - primarily the mythical and primary-source historical material - in the Oxford World's Classics and Penguin Classics series as I can get my hands on and my brain to digest.
I've been thinking about this question for a while. On and off - on whenever the topic crosses someone's blog, as it did a while back; and off when I've other things to do, which is most of the thing. (Really I should be doing some of them even now.) And I've come to the conclusion that there's more than one reason why: or rather, that I read different sorts of things for different reasons. (It would be a more elegant construction were I able to put it in ancient Greek: houtōs dē anagrafō toutous men hōsper legō, huper toutōn logōn, toutous de allous huper toutōn allōn - or at least I think that's how I'd put it.)
The first reason is for comfort: to distract my brain from stressful thinking, or to provide undemanding occupation in the absence of proper, coherent thought. When I read for this purpose, the books tend towards the lowbrow. I'm not necessarily reading for style and grace, sometimes not even for plot or logic: I need a book that will hit enough of my narrative kinks to carry me along, with interesting character and ordinary prose, and enough of a eucatastrophe about them not to perturb my emotional equilibrium. They have a simple palette of emotions, and don't require excessive consideration either on stylistic grounds or for the choice of moral evils; sometimes they're just pure trope and string, but I prefer a higher grade. Examples of the good kind include Kelly McCullough's Broken Blade, Elizabeth C Bunce's Liar's Moon, Rae Carson's Girl of Fire and Thorns, anything by Tamora Pierce, Tanya Huff, Jim Hines, Carrie Vaugn. More complex books sometimes arrive in the comfort category through long familiarity: Lois McMaster Bujold's Curse of Chalion and Paladin of Souls are among these.
The second reason combines aesthetic with emotional pleasure. These are more complex books, requiring concentration and a certain amount of focus. The joy here is seeing a good thing intelligently done, with style and verve and attention to detail: with characters facing hard choices, with realism and freshness and attention to choice turns of phrase, juicy bits of language, and cascading, complex what-ifs, in SFF - and enough of a visceral hook to kick me in the metaphorical squids. (Elizabeth Bear does this to me regularly. Steven Brust on occasion. Marie Brennan, Chaz Brenchley/Daniel Fox/Ben Macallan: Above and The Bone Palace did it in a massive way, and so in a way did The Cold Commands. Anthony Burgess reached the shining pinnacle of this in A Dead Man In Deptford.)
The third reason is primarily for aesthetic pleasure: the joy is the language above all, the execution: my emotional connection is slim, only intermittently present, and I find this to be the case for most of literature-so-called, though the brilliantly-crafted language of Chambers, Burgess, and Durrell appeals to me on the level of appreciation-for-excellent-craft. But it requires some effort to unpack, and as a result I read this sort of thing seldom.
The fourth reason is intellectual. Curiosity. There's aesthetic pleasure in the good history books, and emotional satisfaction sometimes too (not to mention in the Classics series) but it's the grand satisfaction of knowledge that brings me back to the history books: knowledge, and a fascination with cultures and times and places not my own. People are fascinating, and complicated, and weird - and so are the social systems which they make and take part in and surround themselves with.
The fifth reason is work. Do you find it odd I should say so? But since I've started reviewing for paying publications - and especially since starting the column with Tor.com - I've been pushing myself to read things I otherwise wouldn't have finished, and to start things I otherwise wouldn't have read, to have more context for my opinions. (Context is important. Proper understanding of context is perhaps the most important thing, in analysis. It's certainly up there.) (And also because if I say I will review a thing, there is contract of expectations there. Can't stop halfway through and say, First half sucked, so I stopped.)
There is intellectual satisfaction in acquiring that context, but the aesthetic and emotional dividend varies wildly - and it is work. More work than I expected, if I'm honest. So sometimes lately I might read a book from a sense more of duty than anything else, which I haven't done with respect to fiction since I was forced to read assigned texts in school.
Anyway. This is something of an answer.