When the government can tell you to play along or they’ll go to single payer and put you out of business, what choice do they have? And they are some who declined to go on the exchanges, I believe Aetna is one, so they’re not all playing along.
At this point, Aetna is the exception. The rest have gone along because they were told there would be a bottomless pit of taxpayer money upon which they could feed.
Screw them (with the exception of Aetna).