Like all subjective award voting, NHL Conn Smythes are determined largely by the culture of the times -- who is voting, what values they represent, etc.
In 1976, the Canadiens won the Cup, sweeping out the Flyers, and thus breaking the bad-for-the-NHL mini-dominance of the gooning Broad Street Bullies. You'd think, in a sweep, with the media-favored team winning, that somebody from the winning club would take the Conn Smythe. But since Reg Leach scored an unheard of 19 goals in 16 games and dominated Philly's scoring, voters gave the Smythe to him, a winger.
In the '70s, the Conn Smythe had only been around for 10 years, and maybe voters were more easily swayed into voting for whomever was the statistically outstanding player.
I think the youth-movement, high-scoring early-'80s conversely led to some voter backlash against that style. In the Oilers' case, their free-flowing creative offense style went against the grain of the 1950s/60s'-era voters for these awards. And until you've won a couple of Cups, those voters aren't really convinced.
Gretzky was barely 23 in the 1984 playoffs, had done unimaginable things already, and been amply awarded for it. Mark Messier was like a young Gordie Howe from 1952. He fulfilled older, conservative voters' image of what a "real" hockey player, with toughness and skills, was about.
A similar thing happened with Rod Langway's Norris trophies in 1983 (okay, fair enough) and 1984 (yeah... no). It was the post-Carlyle Norris blowback.
Fast-forward to the 2000s and 2010s and it's a really different mindset of voters for these things, Now, the voters were the people from the 1980s who'd grown up with those young, high-scoring players. Also, the NHL was desperate to increase American fandom out of the Lock-out and get respectable playoff ratings on US network TV. Also, dynasties are over by now, so there's no longer a thought that one Cup by a dominant team will lead to more wins by that same team. Hence, Crosby (2016) and Ovechkin automatic-Conn Smythes.
Point being: If Gretzky was playing in New York or L.A. today and his team won 4 Stanley Cups in five years, he'd probably have four Conn Smythes. But that isn't to take anything away from Messier (or Hextall). Mess was still a deserving winner in 1984, but sometimes there's a different mindset across different eras.
