There's a nightmare scenario where they wait for Johnson or Glenn, and they both turn the Saints down. They're forced to run it back with Rizzi because all the other candidates are already gone.
Usually by that stage, the match has been made behind the scenes and just not announced. If we are waiting long for one of those two, it is just a function of us being forced/asked to wait on the announcement.
Obviously people could change their minds of course, and that of course would suck.