It has 5% to do with that, and 95% to do with the expected return for Tanev in futures.
Tanev will be seriously regressing in 3-5 years, which is when the Canucks can realistically hope to start challenging for anything meaningful. However, the picks prospects acquired in a Tanev trade will be coming into their prime, and one of them might be the piece to take us to a new level.
Even with Tanev, we have been a bottom-feeder for 2 of the last 3 years - and most of our key players are regressing. Why keep Tanev? Just to win a few extra games, and maybe shoot for 80 points? Why not get the assets that may help when it means something? Why continue to meander in mediocrity?
Being a "decent fan" doesn't mean you have to be stupid. The 'trade Tanev' club is full of long-standing, loyal fans...they just also happen to know some simple math.