Seems to go way back to the B&W movie era - men in tuxedos, women in evening gowns and boas - glamorous socialites dressed to the nines, watching a couple buys beat each other up. Sometimes the MC is in a tux. I don’t get how that whole package goes together.
Because humans are social animals, and these sorts of customs are signals to each other that we’re all willing to abide by the social rules our societies follow.