Case in point: Aetna. Via WaPo:
Aetna exiting all ACA insurance marketplaces in 2018
Aetna will complete its withdrawal from Affordable Care Act insurance exchanges for 2018, announcing on Wednesday that lingering financial losses and uncertainty about the marketplaces’ future was prompting it to exit two final states. According to an Aetna spokesman, the insurer will not sell individual health plans next year in Delaware or Nebraska.