The fact that you can do social interactions without mechanics doesn't mean that's the optimal situation, and that there should never be rules for it. By that logic there shouldn't be rules for anything, since you could manage just about anything in an RPG without rules. It's just storytelling around the campfire, right?
Seriously though, do you really not see the value in having mechanics that support a PC who's supposed to be a charmer, or someone who excels at intrigue, without just seeing how witty and suave the player is (in the opinion of the GM, like some recurring audition)? Might as well just do that for everything that isn't swinging a sword.
Can my character pick this lock?
I don't know...can you?
Can my character intimidate this guy?
Well, go ahead, try to intimidate me! If you yell loud enough I guess it works or something. Anyway who cares, I statted out these hobgoblins so let's stop wasting time and get back to rolling initiative already, amirite fellas?