On top of these, a few things with the training process also jump out to me from a "can we attract smart and motivated people to this work" point of view: the sheer cost of medical school that creates an imperative for high pay down the line, coupled with a real chance that you can wind up without a residency match but still owe all that money for school, and in particular the grueling nature of the residency system, currently capped at only 80 hours/week since 2003, because people were working >100 and making mistakes.
There are arguments that these are factors that filter out the people who are not sufficiently motivated, but it's hard for me to imagine there aren't a lot of bright young people who might be interested in medicine, but see one of the various paths that exist today to making doctor-level money with only an undergraduate degree and in an environment that doesn't require a working schedule that actively harms your health.