It's mostly the combination of many factors....to say YVR is better geographically positioned to the western part of the United States is not supported by the facts that there are not a lot more western states routes from YVR than YYC, probably 2-3 more routes. But there are a total of 14 US destinations from YVR while YYC had only 8. And many of those YVR to the US routes are heading to the eastern States. So you could argue that if you add more US routes from YYC, then YYC is equally well positioned, just like YVR.
I would tend to believe that most fundamental reason that AC management is not adding any new route to YYC is still the downturn of the oil industry and its impact to the traffic; the traffic volume from 2014 to 2015 was down significantly, while all other three hub airports, YYZ, YVR, YUL, have maintained 5-6% annual growth rates since 2014, the YYC annual growth rate is down at 1%?
Meanwhile you can not treat YYC as a through-traffic city. In YVR case, it's still a popular leisure destination with more attractive tourism and even residential passengers, Calgary is primarily a work-only destination, with seasonal tourism.
With the oil industry on the slow recovery, debatable if years down the road, it is hard to see the AC management add any new route to YYC in the foreseeable future. I would not bet anything in this year for sure. Any addition of international routes, like MEX or PEK, will be many years away.