Health insurers know their time in the crosshairs is coming which is why they're buying up pharmacy groups and providers, to give their offerings a sheen of actual care.
Politicians get to use them as scapegoats, and there is no way voters in the US accept taxpayer funded healthcare. Someone has to be the bad guy and allocate the limited amount of healthcare resources available, and I see no reason why the existing relationship of government makes the rules allocating the care, but MCO implements them and takes the heat would change.
Traders also seem to think the same given the gains in MCO market caps. Also, all the MCOs have profit margins of 5% or less, so this game of punting responsibility costs relatively little in the grand scheme of things.
At the root of it all is a demand for healthcare that far outstrips supply, and so these obfuscations are useful in making sure certain socioeconomic classes are able to attain a greater share of it than others.