Presumably they could pass along the savings and increase revenue by expanding their market share, or lose revenue to a company that controls costs. I see your

Presumably they could pass along the savings and increase revenue by expanding their market share, or lose revenue to a company that controls costs. I see your point though, and in a given year it might be easier to increase medical expenses by 5% than to grow market share by the same amount. One thing I wonder though, is that even without the 20% rule, if the company can get away with raising rates by 5%, wouldn't it make sense for them to do so? If they started with a 20% margin that would increase their profits by a whole 25%, instead of a measly 5% with the cap, so you'd think the incentives would be even stronger. It seems like adequate competition is the most important thing in a for-profit insurance model rather than having a 20% margin rule or not.