The cool way to show off your legs.
When you think shorts, you think some bozo cleaning barnacles off the hull of a paddleboat, wearing denim cutoffs and a sleeveless shirt and drinking a cheap domestic from the bottle. But when you think cargo shorts, you think cool parties on a yacht where sophisticated people drink expensive domestics from a glass!
The only real question is, where do you want to end up? In cheap shorts washing cars behind the local fast-food joint for pennies? Or shaking the hand of a dressed-down CEO who says "I like your ideas, come see me tomorrow after you change into something more professional" and then laughs with you, instead of at you? One of those places you'll never ever reach if you're wearing normal shorts instead of cargo shorts.
Seriously. It's just how the world is made.