I think it's because they saw a windfall position for themselves not so much as insurance providers but as middlemen between the health care industry and the government.
I don't know how they keep their spot on the gravy train once the feds take over everything, unless it is as a kind of consultant/facilitator/kickback industry...which of course is how the rest of Washington runs.
Consider the role of insurance companies in Medicare: Offering supplemental insurance to cover the 20% that Medicare doesn't cover.
There is a lot of competition in the market, so itis pressumably profitable, even though coverage cannot be denied.
What was it Lenin said about capitalists and hemp?