I think an interview would be completely useless if there no friction in hiring and firing. But it takes a while to get an employee trained and up to speed. It takes even longer to replace a fired employee, as you either scrap what they were working on or you try to get their replacement to pick up where they left off.

More friction in hiring and firing results in more careful hiring practices. I'm not sure how much friction there is in the medical profession but I'm guessing there's less friction there than in software development (not counting politics).