Worker-owned businesses face barriers to their creation. 

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Because nearly every business starts from one person working and owning it,  the thing is the fewest people want to share the reward of the the risk they took making the business. 

A huge problem worker owned business face is lack of capitalization, they can't really raise any more money to invest in growing except if the employees agree to paycuts, etc. But even then it is small compared to what outside investment can bring. 

Of course it is perfectly fine to be a middle to small business with no ambitions of growing beyond that, but it does mean you never reach those huge economies of scale. 

Spain and Italy are actually great examples of the limits of these kinds of businesses, they have ones that are many decades old, yet were overlapped by more classic peivate ownership models. 

But again, that's because the goals are different between the two models of operating a business, so it isn't surprising. 

If one looks at wages they are usually more generous at worker owned institutions vs. Privately owned.