If they aren't seeing patients, they aren't billing.
Right, but 2000 hours per year wasn't traditionally the requirement. That may have changed. The professions have declined over the past 30 years.
For example, before the legal profession went to hell, 1200 billable hours was the requirement. Remaining time was for networking, keeping current, attending conferences, etc. If you billed 1500 hours, you were a rock star and guaranteed to make partner. Enough money was made in the billed hours to pay for the off-meter stuff.
They go to school an unthinkably long number of years and then they're put into a sleep depravation nightmare called "interning" for years
That is true. Medical school and residency are extremely difficult.
before they get to have a career that normally includes "on call time" where they're woken up at all hours of the night to go save someone's life.
Obviously, medicine can't be limited to the 9-to-5 hours, because people get sick all the time.
Regarding the very long work weeks, this problem was at least partially created by the AMA. They've been limiting medical school admissions to keep an artificial shortage of doctors. That has created an environment in which working hours are much more than they used to be.