Honestly, I imagine the sword design choices are just part of the civilisations we've encountered not being rapier-esque. The southern Minos are Roman/Greek-esque, so they probably use the gladius sword design. Smooth, reliable, adaptable. The orcs are more barbarian/Viking-esque so their weapons seem to gravitate towards axes and hammers. I suppose some elves may use rapiers, but most of those we've seen tend to use long weapons. Spears, scythes, greatswords. The kitsune obviously use katanas and suchlike.
I guess a rapier would be more fitting for a culture that indulges in duelling and fancy swordplay, like pre-Revolutionary France.