This is NOT about 外乡人. Major role of PostDoc is to

help Professor get funding for the team through publications of own research, as well as supervising research of graduate students. This gets more critical when Professor is not yet well-established, because the whole team needs to survive including Professor.

Without at least 2 GOOD papers each year, it is hard to justify the cost of PostDoc. Sorry this may sound harsh, but it's the way it is.