Lots of studies have shown that the US spends a much larger portion of our GDP on healthcare than other countries, there is plenty of money to solve this problem already allocated to healthcare. I am aware that Medicare does aggressively negotiate prices, and our current system is a complex mess of different parts of the system subsidizing other parts to keep hospitals somewhat solvent, but this is largely just to enable all of the useless insurance middlemen to take big chunks of the money for no good reason (and its not all yacht money, its also just bullshit jobs that accomplish nothing productive but are sufficiently complex to require expertise, training and pay decent wages in many cases).
And I do know that you mentioned a real material reason why this isn't pushed harder by either political party despite the nearly inevitable massive savings if we pull it off. Causing an upheaval in the job market by removing a bunch of unnecessary admin work has real short-term impacts that will be hard for any US political party to weather well. That being said, I do think there are very real paths to achieving this and rhetoric about needing to copy-paste big parts from other countries distracts from how achievable it is. 90% of the work is already there with Medicare, and expanding the list of covered drugs and having a price negotiation with hospitals to make Medicare a good customer rather than a burden in some cases is definitely possible with some political will. A public option if it had been included in the ACA would have likely moved us a lot closer to universal coverage, especially if the mandate was still enforced, and likely would have spurred some of these necessary discussions.