If they want to go vertical the whole way, then retail pharmacies are also not a money maker (see Walgreens’ figures, and CVS pre Caremark and Aetna merger). Then there is getting into the provider side, such as employing doctors and owning and operating hospitals. This side has more margin, but is very liability heavy and very risky to get into.
And Kaiser Permanente already does the entire healthcare vertical, but even they are not able to offer measurably lower premiums.
The biggest margins are in pharmaceuticals, but that requires billions of dollars in investment and many years to develop, all for what? At the end, you might as well sell your own medicines at a high margin.
I feel like a lot of the costs in medicine have to do with liability, and without tort reform, there is not much any business can do about costs.