It could just be tradition and the effects of history. But then why did US history create more shareholder corps while European history created more co-ops?
It could be that US investors are less willing to invest in co-ops. But then, why? Is there something about them that makes them less competitive? Why are they ostensibly worse in the US than in Europe?
My, admittedly uninformed, guess would be it has to do with 1) there are more worker protections in the EU than in the US and 2) Co-ops tend to pay employees better wages, have better benefits, etc.
Shareholder corps will try to drive down their labor costs as much as possible. Walmart goes so far as providing advice to how it's employees can best apply for food stamps, all the while keeping them under the 32hr/week threshold that would require them to receive benefits. This can provide a price advantage against co-ops who are not running these same practices. It the EU the labor protection laws are better so the potential difference of labor cost is diminished between sharecorp and co-op.
Europe had very strong socialist/non-capitalist political movements in the 19th century. Co-ops were seen as one alternative to capitalism, and were a huge movement.
For example in Finland the largest bank and largest retail chain are (consumer) co-ops, and in general co-ops are big players in the economy.
What investors?
2. Cooperatives tend to be more resilient in times of crisis:
https://onlinelibrary.wiley.com/doi/10.1002/jsc.2393
My reason for asking that question in the first place is that 'investor' isn't a role I associate with a worker-owned enterprise. The workers are the owners are the investors, so the statement reads as invalid to my mind.
The co-op movement arose as a reaction to industrialization and capitalism, which threatened many workers. You could understand it as capitalism based on membership rather than ownership, or as a third way that's neither capitalism nor socialism. But just like socialism never really took root in the US, other alternatives to capitalism didn't fare that well either.
Or you could say that they are co-owner of their means of production. So, as business owners, are they actually the ultimate capitalists in disguise? :-)
In general, self-employment is quite a different thing from owning of means of production that other people work.
They were oligarchic rather than democratic: only masters were full members. They were monopolies rather than competing in the market: you had to be a member of the relevant guild if you wanted to do business. And they were not businesses: each master ran their own business instead of working for the guild.