What evidence is there that they do that? That would be a very one-dimensional competitive strategy, given a competing insurance company could wipe them out by simply being more reasonable in handling insurance claims and taking all of their market share.
There is no evidence that this what's happening, and the famous RAND health insurance study showed that health outcomes have almost no relationship with the healthcare system, so you'll need to look elsewhere for explanations for the U.S.'s relatively poor standing in life expectancy rankings.