Each business does a small part of the whole, buying and selling what they need from other businesses.
The reason these networks don't come into existence is the problem of how an interdependent network gets bootstrapped. For example, suppose that gadgets are currently made by a large corporation, Acme, because making a gadget requires designing and making a widget, a vidget, and an xidget, a design for how to put the bits together, and the final assembly, and that is too much for a lifestyle business, and Acme doesn't buy or sell the parts as the whole process is vertically integrated. If there were widgets, vidgets, and xidgets on the market, and designs for building gadgets from them on the market, then there could be lifestyle business building gadgets - and likewise for any other part of the supply chain being removed. However, without any lifestyle gadget makers, there will be no demand for widgets (unless they are useful in another industry).
Maybe there is a business model for helping to bring a network of interdependent companies into existence simultaneously.