We don't. History tells us linemates with the top players are mostly replaceable. We're talking Ryan Strome to Filip Chytil. Not Ryan Strome to Tanner Glass. We're paying 11M to Panarin because he is that type of player that can lift up his teammates and make them perform better. Why are we rushing to pay the first guy he's played with here that did that? And why are we expecting it to continue? It's also generally not good to pay someone with the logic being "he plays well with player X" because now if something happens and player X gets injured the guy you just signed has his value tank since he can't do it on his own. If there was no salary cap by all means go ahead and sign him but every contract has an affect on everything else.
Additionally Panarin and Strome are likely not going to continue to shoot at 11.9% which for reference is better than Sidney Crosby has ever done in a somewhat full season (he beat it twice in a 22 and 36 game year), better than Connor McDavid has ever done in a season, better than every Nikita Kucherov season, better than every Alex Ovechkin season, better than all but one Malkin season, better by 2.7 points than he himself did with PLD in Columbus, and better by 1.9 points than he and Kane did together in Chicago.
I'm not even saying the replacement happens to be Chytil he's just the logical guy since he's already on the roster, can play center, there are no good FA, and the next guy on the roster after him is much worse.