I'm the author. A question I have is: how did so many prices ever get negotiated in the first place? What kind of systems are in place to do this kind of micro-negotiation?
When it comes to large parties, multi-practice groups, health systems, etc, an overall fee schedule or charge master for an existing institution is typically not renegotitated line by line every year but as incremental changes from the previous. Many/most of the parties involved have been working together for decades, some even longer.
Many plans administered by familiar names like Anthem are actually funded and controlled by the large employers the plan services. In those cases the employer plays a role in defining what will and will not be covered and what will be paid and the insurer is a middleman (acting as a third party administrator).