Most professors do not have >>1 postdoc in their careers, because most of us teach at less research-intensive (or entirely teaching-focused) schools that have no postdocs at all. The way things work now, even to get a liberal arts school job requires you to do a postdoc first (at least in my corner of STEM). Anyway, professors at research-heavy postdoc-having schools could get away with more than one. But certainly the status quo is insane, you will hear no argument from me.