The trench coat, though certainly stylish in its own way, is incredibly under-appreciated for its practical values. Consider the basic form of the trench coat. If reduced to its barest principles it is a comfortable, warm, weather-proof covering that comes at least to the knees and contains lots of useful pockets.
Consider the fundamental usefulness of such an item. Wearing a suit and don't want to get it dirty on the way? Wear a trench coat. Get splattered with mud on the way? You're still fine for when you get there, and the coat should brush of much more easily than a suit will. Cold and rainy? Standard jackets leaving your legs cold? Trench coats again, with a nice layer of protection going down to the knees or lower. Need a place to store all your various accruements without lugging around a bag? The trench coat's voluminous pockets provide locations to hold phones, maps, glasses, pens, multi-tools, small children... well, alright, not small children, but you get the idea. And so, I beseech you, do not deride or praise the trench coat for its subculture popularity; do not consider it as a mere fashion item. Consider it for what it truly is: perhaps the most useful piece of clothing ever designed for urban living.