The New York Times blames “guesswork” by insurers.

Wrong, writes Seth Chandler:

If you actually read the justifications for the premium increases submitted by insurers and their accompanying actuarial memoranda, you can see there are two dominant themes: (1) higher than expected claims expenses and (2) diminution of federal subsidies to the insurance industry. You can also see lengthy memoranda containing facts and figures explaining their experience last year and the basis for their trending those experiences into the future. And, while one need not invariably take the insurance industry at its word or at face value, this is an instance where they have to make the best case possible for their rate increases. Regulators will scrutinize insurers’ work. Misstatements or rank guessing would seem to be against the insurance industry’s interest. . . .
Health insurers now have a decent feel what it is going to cost them to participate in Obamacare. And these insurers have a pretty common perspective: the whopping increase are driven by greater utilization than expected among those electing coverage (adverse selection and moral hazard), increases in the cost of medicine, and reduction of federal subsidies.
Exactly what some people predicted.

Via the 2017 Project.