Leafs had to give a first-round pick just to dump a 1 year of Patrick Marleau.
Hawks are better off with keeping Seabrook for remaining of his contract because it'll be expensive to dump 4 years of Seabrook.

Montreal declines, You aren't going to get rid of that Seabrook contract that easier. You might as well buy him out unless you are willing to throw in a young stud for him.

Haha, Montreal largely declines. I don't mean to be a dick but man that is bad! Just because Seabrook is horrible and his contract absolutely sucks.

Let's say there is a GM out there who wants Seabrook as their bottom pair D/healthy scratch guy. If the Blackhawks retained the max 50% of his salary/cap hit of 6.875M, the other team is still on the hook for 4 more years at 3.44M times 4 years for a bottom pair D. There's cheaper options available for the other team. And it's not advantageous for the Blackhawks to keep 3.44M of dead cap space for 4 years.
By the time one makes it worth the other GM's while to have a bottom pair D signed for 4 seasons at a 3.44M cap hit, we're talking about sending valuable prospects and picks while the team is in a rebuild.