Because of that such company will either stay small (probably leaving ambitious people with unfulfilled ambitions) or change along the way, because you simply will not find enough people to make it grow.
It's been a few years since I pondered this, but I used to spend a lot of time thinking on this subject. I think for it to be successful you need a lot of the type of person that prefers to work in such an environment, and to make effort to keep it that way. That might mean staying small staffed, but I'm not totally convinced it even needs that.
One could argue that social economic systems, at scale, are functionally similar to a massive corporation operating on a flat environment. And you end up with a similar issue there. "Company" ambition doesn't really have a viable path forward, and so the optimal solution is to just coast by - and direct your ambition towards your own personal stuff. Or even set the ambition aside, and just enjoy life. At least until the consequences of everybody operating under a similar system of demotivation kicks in.
Once you can break away from many traditional imaginations of what a business is and how it should run there are some interesting possibilities.
Very challenging and easy to get wrong though I'd guess.
https://itrevolution.com/articles/radical-enterprise-pioneer...
And that is true even if the group is the best people possible. The only way would be to have no disagreement, but then you would probably be creatively dead.
To put another way, i suspect communication scales quasi linearly with managers, but at least quadratically without.
Somehow that works, so maybe that suggests ~50% of employees at a business could be in self-organising units of less than 10 people?
And while they may have support staff, they typically "work alone" in the sense that there's one partner per account, so very little oversight or management is needed.
The primary purpose of this "collective" is to create a "brand" of sorts. Ernst and Young has more prestige than say Franklin and Franklin. This draws in higher paying customers.
I feel like there are sufficient differences in this kind of business to a typical software business that the comparison is not especially useful.
Which is not to say that a coop can't work, just that the comparison to accountants and lawyers doesn't work.
My brother is an attorney in a small practice of 6 attorneys. They are all partners, share ownership, and rotate who the managing partner annually.
Realistically, you may as well talk about it as something that can't be done. If anything, it's probably easier to stack eggs than to get more than 4 people to work collaboratively without the current incentives and rules making it all hold together.