Business schools are setup more like trade schools to teach marketing, finance, management, and accounting. Those have little to nothing to do with how to create a product, how to get your first customers and so on and so forth. Most business schools presuppose and existing, successful business of some sort. Take away the existing business and most of what they teach is not terribly useful.
Also, the best teacher of entrepreneurship is not school at all. It is experience. Starting a company, incorporating, getting customers, building a product, hiring workers all seems impossibly hard and confusing at first until you get some practice. Starting a business isn't hard, but it's a much different experience than being an office manager or accountant at a fortune 500.
I learned more starting my first company about how a business should be run than I ever did sitting in classes. There is no class that can teach you how to start a business unless it actually forces you to start a business.
Running a business should be taught like an art school or a culinary school - by doing. Try learning how to cook by just reading recipes or watching cooking shows, but never actually cooking a dish by yourself. Sounds absurd right? Ok, try learning how to start and operate a successful business without ever actually starting or running a business.
That is what business schools do and that is why they fail.