The Face Is the Variable, the Move Is Constant
The reason the challenge crosses every culture is that it only lets you change one thing.
One variable: a dance challenge that freezes the body and the beat, and leaves only the face open, is a template that anyone anywhere can plug into. A soccer fan drops their favorite striker, a K-pop fan drops their idol, a kid drops their dog. The move - the shoulder jiggle on the dembow downbeat - stays identical. That constancy is what makes every version instantly recognizable as the same trend.
Why the face does the work: the joke of a face swap is the contrast - a still, serious, famous face on a body that is going slightly out of control. Messi's face on the dembow body is funny because Messi does not dembow. The body is the setup, the face is the punchline.
How the game locks it: the Shoulder Battle gives you the face library - stars, celebrities, animals, memes - and the body is the fixed Bulin 47 silhouette. You are only ever choosing the variable. The rhythm bar is the move, and your job is to drive it on the beat.