The article explains why; regulators sometimes can't foresee that their decision to consider something fee for service will eventually prevent it from being considered as a communal expense.

Fee-for-service doesn't prevent ambulances from being considered a communal expense, it just makes sticky. There is nothing preventing a government from making ambulances equivalent to fire or police except the will.

From the article: "The most efficient way to fund ambulance services would simply be to pay for the option the way that options are normally paid for: with a premium, collected from everyone the service stands ready to rescue". In other words, taxation just like anything else we expect to be available to anybody.