Edit: not sure why the downvotes, that’s the reality of things. If you want a more fully fleshed out thought, here you go:
We would all contribute to the payment of expensive operations via taxes in a single payer system. In the current system we have insurance payments. It’s effectively the same, paying a small fee regularly, to subsidize the costs for expensive procedures for yourself and (surprise) others. What do you think happens if you pay into insurance your whole life and never need an expensive operation? You’re subsidizing others. Otherwise the insurance companies would be out of business.
But with single payer, we cut out companies in the middle pulling a heafty profit for effectively the same system as we could get via taxes.
Better?