If he extended for below market rates, say $10 mill per year. Then you would know he really wants to stay there and win, not stay because of the money. It would give TML more money to attract and keep other good players. Like when Doan signed for less with the Coyotes, he wanted to stay in AZ.
Players think they can win regardless of the team, except for a few doormats like the Coyotes or others in a rebuild. Mathews is the top paid NHL player, he got as much as he could get, good for him, I would do the same thing as would almost all other players in their prime that are top 10 NLH players.