Even if everything was worker-owned, markets present problems. Through luck and circumstance, some buyers and sellers will have an easier time to the detriment of others. Some will be priced out. Wealth and power will concentrate. With that comes regulatory capture. There goes the idealist "uncorrupt government."

Anti-social strategies like loss leaders pricing out competitors and price gouging and collusion don't go away with worker ownership.

It's still a system of self-interested parties. Social Darwinism over collective well-being.

... not only vertical relations of capitalist exploitation based around the wage labor–capital relation — capitalists exploiting their workers — but also horizontal relations of exploitation — wealthier firms exploiting poorer firms. Horizontal exploitation can occur even between worker-owned cooperatives, which leads you to argue that market socialism may be exploitative in much the same way capitalism is.

https://jacobin.com/2023/02/nicholas-vrousalis-exploitation-as-domination-interview-capitalism-labor-justice