This is probably also a function of all the doctors’ offices that have opted out of Medicare. Fewer and fewer providers will accept it, so many people have nowhere else to go. Also, I don’t know about Medicare, but regular Obamacare drastically shrinks the geographic coverage area. If it has done the same to Medicare, and there are no offices that accept Medicare within the coverage area, then these people have no choice.
And, Medicaid charges no co-pay for the ER, but charges one for a doctor’s visit (minimal, like $5 or so).