Not everybody does. But also, not every man can grow a decent one; it will grow in heavy in one part of the lip and very thin in another. Or it may not match the hair color, which gives an odd look. Tyrone Power (old-time actor) with black wavy hair tried to grow his own mustache and beard for a pirate movie; his facial hair came in RED. And since beard hair is notoriously hard to dye (or so I'm told), they hired another actor for the role, feeling that most of the audience wouldn't believe it was a real beard. Anyway, those men who CAN grow a decent, "balanced" mustache that looks right, they tend to feel it is an accomplishment -- and in a way it is.