"The market for sneakers is booming, driven by millennial demand and a strategic business approach by the major players. According to SportsOneSource, the international sneaker market has grown by more than 40% since 2004, to an estimated $55 billion."
Full article: https://www.forbes.com/sites/deborahweinswig/2016/03/18/sneaker-culture-fuels-1-billion-secondary-market/#6cf424267911