Why aren't there more worker co-ops?

Even when I was living in a very liberal area, there were only a small handful of stores that advertised as worker co-ops. It's funny too because those co-op stores were all incredibly popular and successful, so I don't understand why they are so comparatively rare? The organizational structure seems simple to maintain, and has a high incentive for regular workers to go above and beyond since they directly benefit from the business being successful, so what's the deal? I am speaking from a US centric view, so maybe things are different in Europe, but even with my limited knowledge I feel like they are relatively unpopular there too, but maybe not? I dunno.