I think it’s because in the USA residents can work 80 hrs/week (often surgery residents work more than that and don’t report it) which is a recent development previously I don’t know if there even was a limit. In UK and Australia (correct me if I’m wrong) residents don’t work such long hours which is part of the reason why the training is longer in those countries. I have a family member who trained in the UK before coming the US and his residency working hours nearly doubled when he came over. Also we have to complete high school then undergraduate (4 years) then medical school (4 years) which is a total of 8 years post-secondary school training, whereas I know someone in Australia just went from high school to medical school. A lot of our basic sciences are covered in undergraduate so in medical school we can devote more time to clinical understanding and clinical work. We rotate through all the major specialties while in medical school (functionally an internship as it would be seen in the UK, India, Australia, etc.). In the US internship and residency are considered our specialty training whereas in Australia/UK it’s more of a pre-vocational thing before you set your sights on a specialty. Please correct me if I’m wrong! I think it’s interesting how different countries train physicians so I’d love to hear any insight you have!