First of all, the intent wouldn't be to model the real world. We don't do that with combat or anywhere else in D&D, so why would we do it in the social pillar. The point, rather, is to create a reliable, fun to use system that allows us to abstract something like a legal debate or an audience with an unsympathetic ruler or tricking information out of a spy or any other of a number of archtypical "social combat" scenarios we see in inspirational media. But like with combat and other physical things, we kind of want a realistic-ish feeling.