The way it was explained to me, foil evolved from training for duels to the death (body strikes only), epee evolved from training for duels to first blood (hit anywhere works), and sabre from cavalry training (edge is legal, but only waist up as you're often on a horse).

Then they took on their individual quirks like right-of-way.

It's a duel to first blood.

I mean conversely if you drove a blade into someone's foot, the chance they recover before you deliver a follow-up strike is probably quite low.

On the contrary, when your blade is in their foot it’s not delivering a lethal strike nor is it defending you. Driving a blade through bone doesn’t always come out easily. A trained opponent could probably kill you before they even felt any shock.