There's no reason an insurance provider can't manage a guaranteed cost every year. It's basically just an offset on the risk curve.
You could look at health insurance like a buyer's club (we negotiate prices for a large group of customers) plus a true insurance (the unexpected happened, is expensive). The buyer's club portion can be useful in mitigating expenses for the unexpected.
That said, nowhere in here is there a strong incentive to reduce costs (I go into this in more detail in a different comment on this topic). If you really think about it, an insurer just wants predictability, the actual cost is somewhat irrelevant as long as people can pay it. Because insurance is usually "purchased" and subsidized through your employer, you're somewhat disconnected from that price.
Even if you weren't, you don't really have good alternatives. You can choose the private market (often less good plans without as strong a network) or you can choose no insurance at all. These aren't great choices, and frequently when you're making the "purchase" it's very very hard to know what you're buying.
I've shopped around for insurance, it's quite difficult for them to answer, "I think I might need this thing, how much will it cost me with your plan?"
The whole system needs to be rethought. Likely through a combination of forced transparency, mild price controls, breaking up monopoly-like consortia within the industry and forced standardization of some products to make them understandable.