It is a triumvirate, actually. don't forget the lawyers!
I am a lawyer!
Oh, there are lots more: There are the "provider groups," like chiropractors, "behavior health" counselors, etc., who lobby insurance commissions to require things like inpatient alcoholism treatment. Then there are the ideology groups, who insist every policy cover birth control pills, abortion, AND infertility treatment. There's the gay pressure groups, who don't want underwriters to know whether an applicant is HIV-positive.
In P/C coverage, there are the real estate developers, who insist everyone in the state subsidize owners of mansions on the barrier islands or over the San Andreas fault.
And on and on.