That said--hospital management, driven by the insurance world, tries to wring as much uncompensated labor out of the medical workforce as possible. Doctors (including my MD colleagues) do not get together to limit the number of doctors available. That's baseless conspiratorial thinking that doesn't withstand a moment's scrutiny when you understand the incentives at work in American healthcare.
There are limited slots each year at the accredited schools you must attend in order to acquire your role.
Nobody's accusing you of doing it - but the number of doctors is limited
Ultimately, the number of training slots in the current system is limited by MHA and MBA administrators who see training and instruction as subservient to profits, not the doctors who make up the departments and training faculty. Or, more broadly, they are limited by the healthcare operations not being legislated in a saner way. I was just clarifying.
Edit: In no way am I saying "American healthcare is just fine!" only that I actually have had a really good experience using messaging to communicate with my care teams.