Health insurance is complicated because for most people, it's so much more than just insurance. It's prepaying $300 a month so you don't have to pay $200 to visit the doctor once per year. No, I don't know why people do that. You're right that paying $100 a month for "please reattach my severed limbs" insurance is more affordable. Terminology be damned, that's possibly what people mean by "self-insured". They pay day to day expenses out of pocket.

Fortunately, the catastrophic insurance can be pretty cheap, if you choose a high excess.