IMHO the reasons are....
Injuries . Kk, Gallagher, Drouin, Byron, Armia
Goaltending price is average, backup is bad
Poor pk from defence and goalie
No elite star. Top scorer produces 65 points
Team composition is speed at expense of size or toughness
Media, taxes and language prevents acquiring key Free agents
Bad puck luck. Fluke goals still count for and against.
Bergevin has tried to obtain a Tavares, Aho , O’reily Duchene in part for optics and he will not overpay. The path has improved with Chariot, Tatar, Danault, Suzuki,KK, Drouin,Petry. Note the oilers have the top two scorers in the league. How are they doing? And they are not a lock for the playoffs. You need 23 players to make it work.