How is severe sweating of the armpits sexy to some?

Pheromones: The change in the composition and sweat in the armpit at puberty are one of many changes that indicates the person is ready to assume an adult sexual role. Different aspects of sexual anatomy, physiology, and function are more or less exciting to different people, and no two people are the same; many people like a partner who "smells like an adult" when it's time for loving.