So when you do a French braid in hair, you start off with three small sections. Every time you fold over the outer sections, you incorporate more hair into those sections. This differs from a normal braid, which doesn’t increase the size of the three parts of the braid as you go along.
French braiding flesh would require a lot more flesh. Also it wouldn’t look nearly as tidy because the other ends of the flesh (those not in the braid) are not attached to anything (i.e. a scalp) so it would be a loose tangled mess.
There’s easier ways to make something grotesque and cursed.