If you are a government leader and you offer healthcare to everyone, you are now clearly responsible for any failures. But with an MCO in the middle, fingers can be pointed all over the place.
Different formularies and prior authorization rules can be set for different populations. For example, reimbursement can be lower for Medicaid patients (poorer/younger people), so they end up with less access to doctors, and higher for Medicare (older, likelier to vote), so more doctors are available there. Senators can get their own plan, and the military another, and the tech company employees yet another, and fast food employees, and so on and so forth.
This system benefits all the leaders, so it is not going anywhere. In fact, I would bet UK and Canada move towards this.