There aren't enough Physicians, they don't make much and they all seem to be working 12 hour days but being paid a salary that would equate to an 8 hour day.
Doctors see downsides of a universal coverage are mostly about loss of autonomy and increased demand because when care becomes free demand rises along with pressure to expand access without extra staff.
Yeah, having lived under universal care, the dark side of it was atrociously long waits to see a specialist and having a GP who is obviously overworked and barely spends any time seeing you.
There are not enough physicians because we have limited the number of physicians. This was done, in part, by limiting the number of residency positions.
[1] https://petrieflom.law.harvard.edu/2022/03/15/ama-scope-of-p...