That's because health insurance premiums are actually a tax. You're not paying for your healthcare, you're paying for your healthcare plus the healthcare of someone who can't afford it, such as poorer people or older people.

The ACA limited how health insurance companies could determine premiums by restricting it to just someone's age, which means they can't take into account pre existing conditions or whether or not they're about to have a baby. ACA also forced insurers to not charge older, unhealthy people more than 3x what they charge 21 year olds who aren't expected to use any healthcare.

This means the premiums for younger, healthier people are going towards paying for older, unhealthier people. AKA a tax. Additionally, the nation is getting older and there are fewer and fewer younger people to divvy up these healthcare costs.

See this pdf from NJ showing how the age rating factors work:

https://www.state.nj.us/dobi/division_insurance/ihcseh/ihcra...

The ACA requirement for an out of pocket maximum for in network health care also made it so insurance companies have no ceiling per person healthcare spending, so if someone needs $5M of healthcare in a year, then that insurance company is going to have to pay for it, and it's going to have to come from everyone's premiums.

Bottom line is the amount and quality of healthcare people expect to receive is very costly. So if people want health insurance premiums to not go up so fast or go down, they need to consume less healthcare, lower quality healthcare, or they need to increase the amount of healthcare available so prices of the healthcare go down.