I really don't think it is about money at this point. And I don't say that in a bad way. I think both want to be in Dallas and will be in Dallas. I don't see these two players worshipping the almighty buck. I could be wrong but Dak and Cooper just seem to me to be focused on this season and trust the business side of the game will take care of itself. And I think both Dak and Cooper trust Jerry. Maybe they don't want their signings to be a distraction to the team during the season.
My best guess is that Dak especially, and Cooper probably, want to win so bad that they don't want to sign the big contract and lose the drive to succeed during this critical time during mid-season. Sometimes people lose a little of that drive which sometimes comes when you get a big pile of money all of the sudden.
Both seem to me to be big team players.