I think LotR is the model for much of D&D, though. They travel extremely light, and for much of the books it is smaller parties
I recently read Dunbar's book
Friends, and he mentioned studies that a pair is a conversation, 3 people are a conversation, 4 people as well - but 5 or more becomes 2+ conversations. If there are 5+ and one person is speaking, it's not a conversation but a lecture.
With that in mind, splitting large groups into small in fiction is a literary device of convenience. If we are 30 in a room there's no way any single person can keep track of all the different conversations going on. If we described it in writing then we'd pick one conversation and focus on that, at most we might describe a second, "Meanwhile across the room they were saying -"
Now, here's the difference between writing and roleplaying in this respect. In writing we can just have a core group of main characters and not describe the others much. You get this in people's writing about a small village, like Wendell Berry's fictional
Port William - the place has a population of hundreds, but he focuses on just a few characters in each story. But that was a town, a fixed place, and he was telling particular kinds of stories - none of them adventure stories. In an adventure story you tend to have to describe what
everyone is doing, and it would get tedious to write, "and the camp followers followed along."
But in an rpg you can have the main characters and then the faceless mass follow along. The concept of main and secondary characters is even baked into the early rules, with one group of people having classes and levels, and most people being 0-level commoners (or men-at-arms). It's not as burdensome to have them along.
Now we come back to the bit about LotR. Yes, that's in many players' minds when they come to play. But gaming began with wargaming. That's why it's called an adventuring
campaign. Drawing on those ideas and experiences leads to a different kind of play.