Because there is an inadequate mix of health care risks among the group of people enrolled (and the cost of some care such as drugs is rising).
To put it another way, people needing health care enrolled and people not needing health care have not enrolled. To make matters worse the reinsurance and risk payments from government to offset this adverse selection have not been forthcoming as expected and are expiring.
It’s all quite simple For any insurance to work there must be a mix of zero users, and moderate or average users to offset the relatively few but costly heavy users.
In other words some people pay for insurance they never use (which of course, is not unique to health insurance). With Obamacare virtually all ability to have people pay premiums based on the risk they bring to the insurance has been eliminated, but those with the lowest risk can and are avoiding paying insurance premiums.
As long as we allow the current situation to stand there will be significant fluctuations in premiums as insurers try to guess a year in advance the mix of people enrolling in a given health plan.
If you are a bad risk driver, you pay more for auto insurance. If you live in a severe weather area, you pay more for property insurance. If you have health risks or say smoke, you pay more for life insurance.
Why do many people think health insurance can work differently?