That's not hard at all.
You simply force the Insurance companies to only offer coverage that includes very, very high risk ailments for people with previously diagnosed and expensive to treat ailments. Those people sign up raising costs. Costs go up due to the poor mix of healthy vs unhealthy customers, profits go down, plan prices increase and healthy people bail out of the system. Costs then escalate even further as the mix gets even less favorable.
Repeat until the Insurance Companies give up and quit.
Economics 101.
“You simply force the Insurance companies to only offer coverage that includes very, very high risk ailments ...”
But if you don’t do that, how do you insure everyone?