Protections of the ACA include the requirement to submit premium increases for state and federal review, and limits on how much of premiums can be used for anything other than medical costs. This means that they cannot legally "just" pass costs along, and that even when they can those costs are effectively a representation of the limited power anybody has to negotiate with healthcare providers, which is hardly something one can pin on insurance companies.
And of course on top of that, it's inaccurate to say that people are legally required to buy insurance. It's wholly without basis for the last 3 years or so, and even before 3 years ago it's a dubious representation of the options available to people.
I think it's the exact opposite actually. Insurance is incentivized to go along with Healthcare cost increases because it lets them increase their premium and profit. If you have a 10% profit margin and need approval to raise cost, higher healthcare costs overall is the best way to increase your net revenue while keeping the same profit percent.
And of course on top of that, it's inaccurate to say that people are legally required to buy insurance. It's wholly without basis for the last 3 years or so, and even before 3 years ago it's a dubious representation of the options available to people.