If you remove one of legs of the stool, the market becomes unstable and you see price spirals like this.
Jonathan Gruber (MIT econ professor, and one of the designers of the Affordable Care Act) gave a fairly detailed talk about how and why they designed the ACA the way they did, learning from a similar law in Massachusetts: https://youtu.be/2fTHqARiV_Q?si=SRC6Np-rjgUgAe4Z&t=679