I don't think many people read non-fiction for fun. I know there are people out there who do, but I'm pretty sure they don't make up near the number of people who read fiction for fun. I've never understood why that is. Then again, I'm the person who tried to read the entire dictionary when I was younger, and I have a set of Childcraft encyclopedias that I read the entire way through. I'll read practically anything if I find it remotely interesting, and I seem to find a lot of things interesting that others don't. (One time, my friend Summer and I were talking on the phone when bees were somehow mentioned. I wound up on the bee Wikipedia page, and I became so interested that I spent at least the next half hour informing Summer of many awesome bee facts while she tried to change the subject. My definition of interesting is definitely different from most people.)
For me, learning things is fun. It doesn't even really matter to me what it is. If it's new information, I'll probably find it interesting. (I hate bees, but I still spent at least half an hour on that Wikipedia page.) That doesn't necessarily mean I always enjoy school. (Homework isn't the same as discovering information at your own pace.) I do love being able to read a book full of amazing information that I would never discover otherwise, and I've never really understood why other people don't get that same enjoyment. I have so many non-fiction books sitting around that others wouldn't ever dare read because they'd find them boring but just thinking of all the information in those books and the new things I could learn from them makes me excited.
I think school makes people associate learning with boredom, which is just really too bad. There's so much knowledge out there that you can get from books (and that applies to fiction as well as non-fiction), and so many non-fiction books are well-written and incredibly interesting. I think non-fiction in general is greatly under-appreciated. It really is too bad that more people don't read it just for the pleasure of it.