Because a healthcare plan isn’t insurance. You used the correct term. If you want a prepaid healthcare plan that’s fine, just stop calling it insurance since it’s not.

Totally agree it should be available for cash pay.

It's insurance in the sense you have annual out-of-pocket maximums--which is really the key feature for a lot of people. I can cover $5K or $10K for a year but not, say, $100K or more.