Toronto expressed interest in getting down to business on a contract extension in recent months, but the Marner camp was unwilling to engage during the season, according to league sources.
The Leafs wanted to sign a player who already sits fifth in franchise history in scoring for what remains of his prime and beyond.
Marner wasn't ready to make that commitment before Friday's trade deadline passed - not with a world of opportunity potentially ready to unfold before him this summer.
That explains, in part, why the Leafs entertained trade discussions with the Carolina Hurricanes centered around Rantanen before he was dealt to Dallas.
The big Finn could obviously have helped Toronto chase a Stanley Cup in the immediate term, but he also represented an insurance policy in the event Marner chose to walk out the door and the Leafs pivoted to signing him instead.