Do insurers have an incentive under the ACA to let health costs rise? YES, and I'll show you why

In another diary, Democrats need to fight for a Public Option, not just "defend the ACA", I made the following comment

One of the huge downsides of the ACA is that insurance companies have zero incentive to control health CARE costs — in fact, they actually have a financial incentive to allow these costs to rise, because they are allowed (/”constrained”, but that’s a joke) to keep 20% of health CARE costs. 

Some discussion followed, prompting me to write this diary to explain exactly how it works.  In order to see what I'm talking about, you need to ** view things over time. **

Key factors which contribute to rising health care costs:

A lack of transparency as to how Insurance companies set their “reasonable and customary" charges   A lack of regulation and/or checks and balances (at least that I know of)  regarding year over year increases to “reasonable and customary" charges   The natural tendency of doctors to charge a high enough price for their services when they bill the insurance company so that they don't “leave money on the table” as far as the insurance company is concerned

Now on to the actual example …