I don't think anybody is rejecting the idea, it's just that it isn't considered as a default way to build a new organization. And it makes sense since, for a founder, you take on extra risk, put in extra work, and demand a lion's share of the rewards. It takes a special person to do the first two but not the latter.

If people were actively rejecting worker co-ops, you'd expect to see them failing in practice. But what actually seems to happen is, they're very difficult to start up, but once running, run effectively with little centralized leadership.