Insurers aren’t the only ones taking a cut. Drug companies and hospitals get their piece of the pie too.
At least with insurers, under the ACA, there’s a restriction on what percentage of their spending can be on stuff other than paying out medical care (the Medical Loss Ratio)
Hospitals & drug companies are free to charge whatever they like, and when you need what they’re selling, you’re generally not in a position to negotiate.
Anyway, Single Payer would tend to solve both problems, as long as legislators don’t do something ridiculous like denying your single payer system the right to negotiate on prices (like what happened with Medicare - wtf was that?)