An MBA is a business administration and not a method of business creation.
You can understand this by the following example.
Suppose that you have a Bus service plying along the city. You hire a driver, a conductor, and a janitor. Now you are a self employed businessman (in a much smaller frame though.) Next, you have 10 buses plying in the city. You need a business manager to manage everything from the maintenance of buses to the salary of the drivers, janitors, accounting for fuel cost, licenses etc. Sometimes, you need marketing executives to get new partners in new towns to ply more buses etc.
Now you are a small scale businessman and all those managers are MBAs. MBA is a component of an organisation and has nothing to do with the all-round development and with the conceptualisations of business models.
A businessman plants a tree, does the initial nurturing, take risks of drought and excessive rainfall. Once the tree is good enough to live on its own, he hires some people to take care of it.
Hence, taking care of someone else’s plantation with some fruits already grown and a working method about how new fruits come with all the information about seasons etc, is the primary job of an MBA.
A startup conceives an idea, tests the idea, makes a workable profitable business model. He needs an MBA for management and expansion and not for the development of the initial business. A founder lays the foundation, sets the rules, makes a road map. An MBA has to walk on that road map, give his inputs but in the framework of a business model.
Business schools teach you how to run a business. Real experience can teach you how to start a business.