And if that was the proposal, would that be better or worse than the current status quo?
A major part of why it's so expensive is because of government subsidies to private healthcare insurance. No or little public option is exactly what allows insurance companies to go hog wild on their premiums.
The ACA subsidies are simply a bandaid on a broken system which allows insurance to further break the system as they adapt to what people are willing to pay for a necessity.
The ACA is a bandaid, and may be making things worse over time, at least in some areas. But Americans don't see to have the appetite to really change anything. Probably because most voters are insulated from this by good (enough) employees plans.
Any functioning health care system is going to have a "band-aid" exactly ACA subsidies: make sure that those with the lowest incomes can still afford health care. Something in between Medicaid and the full cost. But as we rein in the costs and get healthcare to be a smaller fraction of GDP, the size of the band-aid can shrink.
The US has real problem that require real changes, but the political system is not responding.
IMO, people sense this, grow frustrated, and become willing to take a chance on someone who seems to speak (more) truth, and claims to be willing to pursue real changes.
We are starting to see more moderate mainstream politicians willing to speak more truthfully, and propose policy changes that may not appeal to everyone. But I'm not sure it's happening fast enough.