My best guess to this question is the fact that The Hobbit is a quintessential example of the "hero's journey". While it's not the oldest, first, or best, it's probably one of the foundational examples of a reluctant hero, pulled into a journey by an older mentor, and set off on a quest that both changes him and changes his surroundings. Knowingly or not, the entire superhero genre that's dominated modern summer box-offices borrows heavily from this structure, making a study of The Hobbit a study of everything else.
But of course, that can't be it, right? Why are we reading this story? The class discussions yielded some interesting theories..but the truth remains a mystery. Perhaps there's no reason why we reason this novel (over another). Perhaps, sometimes, it's simply good to read and discuss. That's mostly what makes us humans anyway.