Earlier quoted context omitted.
If insurers’ customers were not price sensitive, then they would have higher profit margins than 5%.
The accusation here isn't that they are skimming a disproportionate amount, it's that they aren't doing their job, which is to put downwards pressure on provider prices.
See pharmacy forums as an example for all the pharmacists complaining about how independent pharmacies are so tough to operate due to ever smaller payments from insurance companies for the past 10 years.