Interview three people for a job. One is ok, one is good, and the other is clearly a better candidate than the other two; better qualified, more ambitious. The clear winner gets the job. That’s understandable. The recruiter wants the best person for the job, but perhaps without knowing it, they are applying a kind of Nash equilibrium. They are assuming that the candidate, once recruited, and themselves have nothing the gain by changing strategies.
But, the situation can quickly change so that the Nash equilibrium no longer applies. Ambitious people are always looking for better opportunities, more pay, more responsibility. If they were your best candidate, chances are they’ll be somebody else’s best candidate. They’ll be offered another job and they’ll take it, leaving you to start again.
But what might have happened if the recruiter didn’t use Nash and instead hired the second best candidate. They might not have all the skills and experience you want, you might have to put more into training them, but they might not leave as quickly. They could grow with the role and actually end up being the better candidate in the long run.