Or, the likelier explanation, is that health insurance prices are highly regulated and have to get their prices approved by a government official(s), and B) they don't have a lot of pricing power due to the competition and they are not colluding.
See almost any of the proxy filings and you will see much of the compensation is based on hitting targets other than just revenue, and most of the compensation itself is equity:
This assumes the competitors are not all colluding to raise prices across the board