My intuition is basically its like networking. Using broadcast on a shared medium works fine for small groups, but in big groups it overwhelms. Similarly, in small groups flat structure is fine, but eventually in large groups you have to spend 110% of your time managing relationships and stakeholders, which simply isn't practical.

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.