I think there's often an issue of how you measure success. Co-ops seem to have much lower tendency to try and take over the world than corporations inevitably seem to display at scale - quite content to return comfortable salaries year-after-year to their employee-owners, rather than reap profits at all costs.
As a concrete example, Mondragon has been operating very successfully for ~70 years, but barely anyone from outside the region registers its existence.
Right, and if this was the enforced model there would be a lot better spread of risk and a lot more competition. But it's Socialism!!!!
Instead we are almost down to one or two grocery chains and the government is left with the impossible task of regulating the consolidation to mitigate risk and screwed prices.
As a concrete example, Mondragon has been operating very successfully for ~70 years, but barely anyone from outside the region registers its existence.