I think there are clearly multiple factors in rising medical costs. I don't even know how to rank them.
1. Provider costs. And even within provider costs, there is a huge discrepancy, mainly between primary care and specialists. The proportion of specialists in the US is very out of control compared to other countries, and specialists simply cost many times that of a primary care doctor. This is also exacerbated by an internet and media that encourages people to assume an issue is not settled until 1-2 specialists say so.
2. Fee for service. The reimbursement structure itself incentivizes rising costs. Even the most well meaning physicians unconsciously err on the side of performing a procedure if it reimburses at a higher rate than just talking about it. And as above, the proportional costs are a bit out of control, such that our procedure-happy culture ends up footing a huge bill for unnecessary procedures.
3. Insurance. Insurance, as a concept, is basically a group of people saying "some of us will get sick and some will not. On average, we will have medical expenses of 10,000 per year. So if we all put in 10,000 per year, and use what we need when we need it, then we won't have unexpected bankruptcy." And if you have a large enough pool of people, it works. These types of systems have some sort of inherent efficiency, in other words, Money In - Money Out. The most efficient systems will have the smallest gap between money in and money out. Medicare/medicaid sometimes look wasteful due to the massive size of the population, but is by far more efficient in terms of money in - money out. In private insurance, there is a huge gap between money in - money out, mainly going into executive suites, executive salaries, etc. Ideally, the money "should" be going to lower premiums (taxes?) and higher output.
4. Pharmaceuticals. Big one. Patent law regarding pharmaceuticals is broken, as is price negotiation law, with laws basically preventing consumers and providers from price comparing, etc. It's really really bad.