The Leafs want to keep Marner.
Despite Nylander being much more mild-mannered and his camp fire quieter than the Marner one, the Nylander peddling by the Leafs before he signed an extension got out and was everywhere. We even know the Leafs were hunting for the best Dman available in any potential return.
So it stands to reason that the reason the Leafs didn't do the same with Marner, was because not only did they know the Marner camp has the full NMC, but there was a 100% guarantee that any peddling/whispering/quiet trade talks trying to gauge the league's interest in Marner, would have gotten out and made it's way back to Team Marner.
And at that point, knowing how they take so much of this quite personally, any extension possibility is likely right off the table.
My read of the trade deadline situation with Rantanen is that the calculus for the Leafs has changed - they are far more desperate now, knowing they aren't going to get him resigned. There really isn't any "need" to gauge the player's interest in a trade. You either like the deal enough that you present it to the player to get a deal done, or you're confident that the player is going to sign / say no, that you simply don't even take it to him.
By not only taking it to him, but by going public with it for no apparent reason, I think was the nuclear option to put all the pressure and focus away from the organization as they gear up for the fact that one of their most high profile players is about to walk for nothing.
