Because their primary purpose is not footwear, it's fashion. Fashion is an attempt to create artificial trends using artificial brand images (decor, color, design, etc.) so the manufacturer can create artificial supply-and-demand curves. Otherwise why would people pay $200+ for footwear? Insanity. They create a trend, then change it periodically so that people with perfectly serviceable footwear will feel the need to go out and buy new footwear.
I can't imagine behaving in this way.
But many people do.
Can't they see how they're being manipulated?
Many arguments can apply to almost every "consumer" item that people go into big box stores or shop online for. Hairstyles, eyeglass frames, clothing obviously, automobile colors (did you know manufacturers rotate car colors and agree on specific colors for each year? in order to make older cars appear "dated" so people will feel they need to go buy a new one). Housewares colors & designs. Furniture and other furnishings. Makeup. Handbags. Luggage. You name it.