UNH is so big because its customer Apple has its own pool. Apple deducts $24k/y for your healthcare. Healthy 29 year old male doesn't use anything. UNH denies the claims anyway. It gives that money back to Apple, which doesn't give it to you.

The 80% rule has a lot of loopholes. It doesn't apply to employer funded plans. There's a reason UNH is so big!