Comment by llamaimperative

You're ignoring the fact that all of the large insurers are increasingly also the healthcare providers.

UnitedHealth Group is the owner of both United Healthcare (the largest insurer in the country) and Optum (the largest healthcare provider in the country).

Part of UHG's low profit margin is its liberal use of intra-company eliminations, where transactions between Optum and United Healthcare get zeroed out and don't count toward profit despite it ultimately generating more dollars in the parent company's coffers.