That's because Shanahan is the one running the Toronto Maple Leafs, and not Treliving. Every thing runs through him. I think success for Shanahan is making the playoffs year in and year out & hopefully one Stanley Cup. Hence their logic and reasoning behind not trading top players and just filling around them.
Also, team isn't fond of trading long term potential players for short term players. Would Toronto trade 1sts/Cowan/Minten for players with term (4-7 year contracts). I think they would, but I don't think they are into trading 1sts and blue chip prospects for 30 games anymore.