A crotch gusset is meant to promote mobility. If you're squatting down or lifting weights, reinforcement in the crotch area is necessary. The gusset seen on both pants allows them to stretch better and ensure they won't rip on you. However, one is more reinforced than the other.
Philippe says: "They have a crotch gusset, but it's very minor. It's almost just to say they can do it. It's tiny and there's no cover stitching at all in the crotch gusset, it's just a single stitch. We do cover stitching on every single seam just to make sure they always hold up. They're not doing it on the inseams or on the crotch."