If Toronto trades Marner, they're likely retaining 50% in order to maximize the return. They could do the same with Tavares, free up $11m in cap space by the draft, replace both players with upgrades while getting back max return, and only need to carry the additional $11m in dead contract weight for 1 season.
Especially if Toronto decides on a one season re-tool, this would be the ideal move and a BUNCH of teams would be fighting each other to get their hands on either player at 50%. And if Toronto approached both guys and said "Look, we're not re-signing you. Can you wave your NMC so we can get a nice return, and you get the opportunity to chase a Cup and possibly preview a team you might want to sign with?", why on earth would either player say no? It works out for everyone.