Why? Robertson and Hintz have supernatural chemistry. You don't mess with that for an unknown. And likewise Johnston and Benn have chemistry with Johnston bringing Benn's game back from the dead.
Yet when the chips are down those are the two who will play together because it gives the team the best chance to win. So why have all these other steps in between? If Lindell-Nils can be as robust as we hope it can be, you can have a 1st pairing playing major minutes, a strong 2nd pair not far behind and a 3rd pair that you hide and plays minimally.