The reason is because Medicare for All is viable both politically and implementation-wise. It's been studied for decades and the bills are already written. Just phase it in by stepping it down: 65+, 55+, 45+, everybody.

All providers already accept Medicare.

The only disruptions will be to private insurance, which is a backdoor white-collar, make-work jobs program for millions of Americans. But most jobs are bullshit anyways. That's a broader problem and we don't need to sacrifice lives to deal with it.