In the case of Dermott, he could decide that playing for the local team is worth enough to take less.
But if I was Dermott I would have a lot of questions. I assume that Dermott is confident enough in his on abilities to think that he should be a top-4, if not now, very soon. Dermott has Rielly and Muzzin ahead of him on the left side. Sandin and Lehtonen are also LHD. Before I would even want to consider taking less I would want to know what the team's plans are to deal with that. In the 24 games that Muzzin, Rielly and Dermott were all in the lineup this year Dermott averaged 14:45 a game with 37 seconds a game of PK time (and that includes a game when Muzzin was injured early in the 1st period). Keefe also played Marincin in the top-4 over Dermott for the first several games after Muzzin's late December injury which I would consider a real kick in the pants. I assume that is not the kind of regular deployment Dermott imagines himself doing for the next 4 seasons. So how does the team plan on remedying that situation, and if it involves moving Dermott to the right, then how can the team commit to that when they haven't seen how he will play there? If I was Sandin I would have these same questions too.
For myself playing on the hometown team would be a dream come true, as I am sure it would be for most people, but I would not pass on the opportunity to reach my potential elsewhere if I felt that my path was blocked. And I certainly wouldn't take less to stay in a place where my path was blocked.