Arizmendi and Cheeseboard are separate companies though, same with Cheeseboard and Sliver (which is btw not a co-op). Not sure about Mondragon's structure since it's headlined as a corporation/federation of co-ops, which sounds like the workers don't collectively own the entire business and there's a higher level that's just a regular corp.
Anyway, I'm not saying co-ops can never expand while still maintaining collective ownership, only that it's harder. Also harder to start, or to exist in general.