I don't like spending this much time arguing against campism but they just keep talking at me.
Because then the workers are just owned by capital when the point of the economy is still to create exchange value.
What happens then is the coops that pay their workers less will amass more capital than the ones that have better working conditions and push the better ones out of the market. When the goal is to generate profit, then a company that is privately owned by a capitalist class is the most efficient at doing that.