Take, for example, PrEP for HIV prevention. Costs about 5,000 dollars a month - insurance is forced to cover it. Sure, you could say HIV is very expensive, but few people at risk of HIV actually get it. If it were up to insurance companies, they'd rather just pay for HIV treatment or even better - just drop customers with HIV. The ACA prevents the latter, and the former was the case for 15 years since Truvada was introduced. Of course, now that's changed too, and they have to pay for Truvada.

This is often repeated, but it's simply not true. Preventive care is better for patients in the long run, but at a population scale it is more expensive than foregoing it.

And that is before you account for the fact that patient churn is quite high (especially since most plans are linked to employment). An intervention that cost money today and may increase costs within the next few years (due to followup care) is much more expensive for insurers if the savings will only be realized in 10+ years, when the patient has moved on to another job and so is no longer on their plan.

Very few medical interventions save money in the short- and medium-term at a population level. That's reflected in the fact that health insurers didn't cover most preventive care until required to by law (the ACA), and even then they routinely simply ignore this provision of the law. If it were profitable for them to follow the law, why would they go out of their way to break it?