To use car insurance as an example, it would be like if we had a government program for cars over 150k miles. You have to pay for both private and government insurance. The private company collects more money than the government, but the government pays for all the expensive stuff because that's when cars break down. It's completely pointless.
If you want a medicare-for-all scheme where working people have a higher cost-share than children/retirees, fine, that's reasonable. Having private companies rake in profits from a system that has no business being a profit enterprise is insane.