In the US, "physicians" might be less numerous, but there are a lot of highly-skilled intermediary roles that fill the gap -- Physician Assistants, Nurse Practitioners, etc, all perform routine treatment performed by "physicians" in other countries.

US physician training is honestly excessively long, complicated, and expensive (although there are justifications for making it this way), but it's a simplification to point out that there aren't as many doctors, without noting all the other doctor-esque roles with significant overlap.