The complexity is far higher than credit card processing, including extensive price negotiation with individual health care providers. Though we call it "insurance" it's just as much a "buyer's club" for health care services.
Large employers (e.g. Google) are also generally "self-insured" meaning that the "insurance" component is offloaded to the purchaser, the employer of the insured individuals. In those cases, the health care insurer processes the claims from health care providers, determines if they were justified, or if the treatment/diagnostic/drug is justified by coverage determinations of the provider, etc, but the employer (e.g. Google) just pays the claims in the end too.
Large employers (e.g. Google) are also generally "self-insured" meaning that the "insurance" component is offloaded to the purchaser, the employer of the insured individuals. In those cases, the health care insurer processes the claims from health care providers, determines if they were justified, or if the treatment/diagnostic/drug is justified by coverage determinations of the provider, etc, but the employer (e.g. Google) just pays the claims in the end too.