A much larger supply of doctors would presumably lower their pay significantly, right? Will people still want to put in the years and years of training to become a doctor if the pay drops significantly?
The USA doesn't recognize those other doctors (in more ways than 1 apparently) and that is an aspect of the issue.
Prestige and potential higher pay for specialisations will still attract people to the profession, although maybe not if the university costs for medicine remain as high as they currently are.