It makes sense where you have a lot of stakeholders. Would you ever debate an approach to doing something in front of a customer?
Likewise, if a meeting is where you adjudicate something, you need consensus to focus on the key issue, whatever that is. Otherwise, you’re likely to head into some rabbit hole that results in no decision.
There still is a semi-democratic process (barring large-scale network effects for the sake of discussion): whether a given person chooses to become (or stay) a customer. People vote for or against a company’s products/services with their money.
Co-ops are usually a republic, not a democracy. People still have specific roles, and those roles have authority to make specific decisions without getting a majority vote for that decision.
I don't know enough about co-ops but it seems to me they not only redefine the power structure, they also redefine what success (for themselves) is and the means to reach it. Unfortunately ou can't directly compare the two.
You're assuming it's the small group of people who make the final decision without additional input. Just because a smaller group of people refine and vet an idea, doesn't mean they force it on everyone else.
The problem being solved is that most ideas are not good, so any single person with an idea looks to vet it among a trusted group of advisors/peers. If this group is too large, it's hard to deal with the noise, too small and it may kill or ok an idea when it shouldn't be.
After refinement with the smaller group, an idea now has enough substance to bring to the larger group and hopefully not waste their time.
A simple example this process helps avoid would be pulling together the full group, presenting an idea, and then legal killing it with their first comment. Everyones time was just wasted since the idea as presented had legal issues and needed more refinement.
Likewise, if a meeting is where you adjudicate something, you need consensus to focus on the key issue, whatever that is. Otherwise, you’re likely to head into some rabbit hole that results in no decision.