Because the Canucks aren't looking to get rid of him, he hasn't done anything to drop his value, and that package is the equivalent of Vancouver offering you guys Leipsic and Boucher in exchange for Liljegren and Holl. How would that sound? Not too fun, would it?
Now, I don't disagree with all that much of what you're saying, but I'd say the comparisons you're trying to draw are a little off:
Woo hasn't done anything to improve his value either. Not that we would expect him too, there has been like 10 games for him post-draft. So, it sits exactly where he was taken, a mid-2nd. You're comparing that to Liljegren, who was a mid-1st, and showed pretty decently in the AHL last year. So, I'm pretty sure Liljegren would carry a lot more value than Jett Woo.
Boucher is 24, and can't crack one of the worst lineups in the league. I doubt he ever becomes an NHL player. Johnsson is a year younger, and HAS cracked one of the BEST lineups in the league. So, while Boucher is pretty much zero value, Johnsson isn't. Now, as Johnsson is 23, I carry no illusions that he'll ever be a star player, but he's pretty steadily progressed, and he looks like he'll be okay in a depth role. that doesn't carry much value, I'm fully aware. But more than zero, like Boucher.
Leipsic and Holl, yes, I agree, they're a wash. Zero value for both of them.
But what you say is true. The Canucks are better off with Woo than Johnsson, as they're better off with prospects and youth right now. Just as the Leafs are better off with NHL capable players, like Johnsson, not Woo. So, that I think almost everyone here will agree on. The trade serves no purpose.