MuhVerisimilitude
Adventurer
But there's a very important component missing here.It doesn't and never has. There's a boardgame called Diplomacy that has a huge social component with no robust rules for it. You and your opponents try to persuade one another to support, attack, betray, etc. the others in order to try and win the game. That social component doesn't obviate the game part, it enhances it. Just like in D&D.
The "diplomacy" in Diplomacy works because the game is set up to function that way. You could remove it and replace it with a system, but, crucially, no system is required BECAUSE the game IS about the negotiation itself. We don't need to put any abstraction in between the player and the game itself, because the player is the player in a game.
But roleplaying in an RPG is different because the player is playing a character. The game itself is NOT about how skillfully you navigate this without rules. After all there are plenty of extremely role playing heavy systems with MORE RULES FOR IT than D&D.
Bringing up the Diplomacy board game is excellent for illustrating something, though. Imagine that you had a few sessions of D&D in which the player characters meet this NPC who's just invented a board game he calls Diplomacy. He wants the player characters to play this. How do you implement this if you were to try in a campaign? It is obvious that the player is not the character.