

If you mean just rely on state-level taxation, it’d create a incentive to work in (low tax) states that didn’t provide state-subsidized health care, then retire in a state that does.
You want any kind of intergenerational wealth transfer to happen at the federal level, else you will tend to get those misincentives.
The elderly have much higher per-capita healthcare consumption than do people during other points in their life.
One element of the ACA was capping insurance premiums for seniors at an 3:1 ratio, where seniors couldn’t be charged more than 3 times the premiums of people at other ages in life.