I'm guessing the economy of scale for such a buy in isn't enough, and that states would have to take out as much debt as their yearly budgets or even more. Even a Elizabeth Warren's proposed solution was something like 17x the federal budget.
FWIW, New York's current Medicaid budget alone puts it between San Marino and Israel for per capita healthcare spending. Widening the net a bit, that's between Italy and the UK.
https://www.heritage.org/health-care-reform/report/how-socia...