Connecting flights commands lower yield than non-stop flights. Hubs need a healthy percentage of originating passengers to sustain sufficient yield, especially for long haul flights that are more costly. Currently AC can route lower yield connecting passengers thru existing hubs in YVR and YYZ, both offer greater connectivity than YYC, and have local passengers who can fill the Business and premium economy cabins at higher yield.
Most hub airports have less than 50% connecting passengers.
http://elib.dlr.de/96939/1/Maertens_...estimation.pdf
Interesting paper! Although a little dated now, I am actually surprised YYC manages 19-20% in transfer traffic. Since YVR is not a whole lot higher (26%), it gives credence to the local market being an important factor. I would have thought transfer would be higher.
I suppose airports like AMS (with transfer traffic > 70%) are relatively rare.