True, but that's great fantasy novels, and as another form of media it is different to RPGs in subtle yet critical ways.
An author has total control over every. word. on. every. page. (That is, before the external editing process begins, obviously). He or she doesn't have other people gathered around a table attempting to interact with each other in an unscripted, un-premeditated fashion and stay amused, meanwhile juggling their true personality and OOC comments with staying in character (if they're bothering to roleplay at all, since we all know some players just play aversion of themselves with pointy ears and a funny name).
A D&D game is essentially hosting a sort of social gathering, and everything that entails. In practical terms, a LOTR equivalent would require a party of NPCs. Real players would fall asleep at all the descriptions of terrain and weather. I almost did as a reader, thank goodness for the movies.
I get all that, but to an extent I disagree. D&D comes in many flavors, and depending on who you're gaming with, it could come in a very linear, story-like flavor. Your plot progresses from the Lands of A to the Forests of B to the Mountains of C to the Volcano of D...oom.
Some are more like those RL Stine, "choose your own path books", in which you have a variety of options, and most will lead to the same, or similar conclusion. But you have a lot of ways to come about to that conclusion, and the choice, however much an illusion, makes it interesting.
And of course, some D&D games are very much the "social sandbox". Where you are given a world, in which danger may exist, but you have to go out and find it. You're told nothing unless you look for it and at the end of the day, you could spend all night in a tavern drinking until you turn green.
The DM however, always maintains control over the game, and through the use of NPCs, plot events, "wanted posters" or what have you, can move the game along. Yes, there is some "democracy" to the game, which allows players to have control over what they do, but there is also some dictatorship that allows the DM to push them out into actually doing something. So in some ways, D&D is like a book, and in other ways it isnt.