The uncertainty comes from not knowing exactly what services will be performed, who will be performing them, and how much the insurance company will cover (which has a ton of variables, many of which aren't known until everything is settled).
In my opinion, getting away from the fee for service model is one of the routes we ought to be taking to address healthcare spending in the US (if you're charging per service, you're incentivized to perform as many services as possible in a given encounter).
In other professions if you make a bid and fail to capture required work, you eat it generally speaking.
Contractors, many of whom are small businesses or individuals, do this all the time. They also give estimates like "If we find mold behind the wall, it will be an extra ten thousand".
Medicine is also odd in that you have to pay for the doctors mistake. If the doctor prescribes a less effective drug, it has no effect and then after doing your own research find a better drug and get the doctor to prescribe that instead. You still have to pay for the first visit. If a plumber decides to go from plastic to copper pipe mid job, he doesn't get paid for the work he ripped out.
Multi billion dollar hospital groups, full of highly educated professionals apparently can't pull this off but the guy who poops in a bucket on the job site can.
The most insane part are the out of network professionals. It's like you have a deal with the plumber to fix tout kitchen for $100. But in the middle of the fix, you hear a surprise ring in a front door and it's a helper of the plumber that comes an does something. And the next day the plumber notifies you that you must pay an additional $500 for the other guy.
The hospital is reimbursed on a fee for service basis. Most (all?) countries use a fee for service model, but most countries also don't have for-profit payers that are incentivized to drive up the cost of care.
