Why do bishops always have a disdainful expression on their faces? Why do pawns have big globe heads?
Well I know the pawns have "Round" heads to mimic the helmet of the medieval foot-soldier or pikeman (who were drawn from the "commoner" class and were not nobles or Knights -- see this https://www.darkknightarmoury.com/p-3111-kettle-hat.aspx for reference). The foot-soldier's helmet was also known in England as the "Pikeman's Pot."
Of course in the English Civil war the Puritan side, consisting of mostly commoners versus the King and Nobles, were called "Roundheads," but that was more in reference to their haircuts ("Beatles"-ish bowl style as opposed to the long flowing hair of the Nobles and Knights.)
Just when everything was going good a scholar jumps in.
If they used unicorns, we'd be discussing horns.
And then before you know it everyone would be yakking about Trumpets.