That's not what we're talking about.
What people are proposing here is literally that hospitals are eschewing short-term profit in order to increase the expenses they have to pay in the long-term (physician salaries).
Pretty much in any industry, participants could collude to reduce supply to keep up prices. In practice, such arrangements are highly unstable, because individual participants have huge incentives to break rank and seek short-term profitability. What makes you think hospitals are different?
In addition to everything you said (which is true), in this case, the hospitals and doctors have opposing incentives. I can't imagine why hospital administrators would collude to increase their expenses (ie, their employees' salaries).
When Apple, Google, etc. were found to be fixing wages, they were trying to keep salaries down, not bring them up.
If it is the case that the author has intentionally neglected to mention other factors that contribute to a resident being a cost center, I would sincerely be interested to learn about this.