I would assume this is related to the economy in Alberta? Fewer workers heading to the oil fields, perhaps? Vic-Edm has traditionally been a staple with multiple carriers operating non-stop flights.
Prior to summer 2018 with Flair and Air Canada service, and summer 2017 with NewLeaf, the YYJ-YEG route had been solely operated by WestJet for many, many years. Air Canada was the last operator prior to summer 2017, when they did a single summer seasonal Edmonton flight in summer 2007. So basically we went 10 years with just WestJet operating regularly scheduled YYJ-YEG flights, and even before then it was still just WestJet aside from that summer 2007 season.