lack of mass production probably and cuthroat capitalism. the expensive bikes cater to a niche of bike riders who the business knows can afford to buy them. a lot of these bikes have specialized parts made in specialized countries by craftspeople which up the price of production and in addition they offer some kind of free maintenance you are also buying. the real question is why are cars and other bike so cheap, and thats because of mass production factories and cheap manufacturing methods and economies of scale