I don't know what's stopping them. We have a very successful co-op bakery in Detroit called the Avalon Bakery. They make awesome bread. The company was founded by a bunch of hippies who pooled their resources to start a business. It's successful partly because of the high quality of their bread, and partly because their prices are still lower than Panera Bread's prices. Also, they sell their products to the local restaurants, and a couple of suburban grocery stores also carry their bread.
They worked hard to build their business, however. I'm not sure that the OWS protesters are capable of that.