But they were basing their initial design on things that already existed. One was Chainmail and other wargames, but the other was genre. Lieber and Howard and Tolkien and Vance and Lovecraft and so on. The game was designed with those stories in mind...so rules for fighting were definitely necessary because those stories all included fighting, or the possibility of it, at least.since the game appeared in 1974, well within living memory, it clearly came first. Of course, it was preceded by Chainmail & other wargames, which carried with them an expectation of being combat simulators - but, for the most part, that wasn't /our expectations/ as Roleplayers, because we didn't exist as a community until after D&D came on the scene.
So the stories influenced the game design, and then the game design influenced the stories players told with their game.
So why is a specific game so combat heavy? Because Gary designed the rules that way? Or because of the genre the rules are meant to reproduce?
I feel like it has to be a bit of both.
A murder mystery is a great example of a genre that wouldn’t really require combat mechanics. There are others, as well, but even within genres we’d typically think must have them, there may not always be a need. I’m thinking of fiction where most of the “action” occurs offscreen. Or where it’s minimal. Something like The Wire, let’s say. Five seasons of cops and drug dealers, and there are very few gunfights. Rome had almost all of the warfare take place offscreen, although it did show more small scale fights.There are reasons a game /could/ be more focused on combat, like it's a combat simulator, or the stakes of combat are life-and-death or combat is always there as a last resort - negotiations break down, exploration triggers hostility, whatever. But no reasons it must or should be, and reasons it might not be: combat could be out of the scope of the genre, or instance, or a (comparatively) minor part of it. In a murder mystery genre, for instance, violence is actually pretty rare, overall in what would correspond to play - there's /a/ murder, which is viewed as a terrible thing, but generally happens 'off stage,' anyway, and the murderer rarely fights his accusers (more often confesses, gives up, flees or dies trying), and it'd be an odd twist if he got away with it by resorting to violence.
These shows were still very compelling. I don’t know if there’s any reason that a RPG couldn’t replicate such fiction.