[Aunche]

Even if you solve the problems that other people mentioned, there is simply very little incentive for a successful co-op to hire extra workers to share their prosperity. For example, say a co-op has ten people and sells 100 widgets at $100 a piece for a $20 profit. However, their widgets are constantly out of stock. If they hire 5 more workers and sell twice as many widgets at the same price assuming economies of scale, now each worker may make $30 of profit. However, it would be much easier and more profitable for them to simply raise their prices to $120, and make $40 of profit.

[bombcar]

coops work best in cases where the product is relatively easy for competitors to start their own coops; things like farming, building, etc.

[indigochill]

How's that a problem? Co-ops' purpose isn't job creation.

[Aunche]

It means that co-ops will usually lose out to traditional companies in economies of scale. If you somehow force all companies to be co-ops, then you simply end up with the same in-group out-group dynamics as capitalism except everyone is worse off.