Imagine the government creates a prepaid food program, lets call it "Foodcare," only available to a certain population.
The Foodcare beneficiaries pay a little for their coverage, but the government also taxes everyone else to fund Foodcare.
Those taxes make it so that Foodcare beneficiaries get $3 in food for every $1 they paid in. In fact, Foodcare beneficiares are so powerful a voting block, that the federal government will borrow large sums of money just to ensure the Foodcare beneficiaries continue to have access to all the kinds of food they want. Lawmakers make sure they maintain that subsidy so Foodcare beneficiaries can get three times the amount of food as they paid for.
Meanwhile, Foodcare doesn't pay chefs or restaurants very well, but they need to stay open for Foodcare customers. If they don't allow Foodcare customers, they lose the ability to take walk-in patrons. So they calculate that they need to charge private customers a lot more so that Foodcare customers can eat off the same menu. Giving everyone Foodcare prices would put everyone out of business, so the private paying customrrs need to further subsidize Foodcare.
Of course, Foodcare is popular! Foodcare beneficiaries are getting steak and lobster, subsidized by private paying customers through higher taxes and higher prices.
"Let's give Foodcare to everyone!" they say.
But wait...
It's a mathematical impossibility for everyone to get subsidized access to food. Some people are going to pay for a whole lot of food they don't eat in order for others to eat more than they paid for. That's just basic math.
So Foodcare is going to need to pay chefs and restaurants a lot more. To keep from going broke, it's going to need to strictly limit what people can order on the menu.
"No more steak or lobster," the waiter says. "The approval process for those takes months. Government bureaucrats need to authorize every item you order. Would you like some gruel instead?"
Now, all of a sudden, Foodcare isn't so popular...
And yet Medicare is more popular than private health insurance.