Hart trophy goes to the Art Ross Trophy winner in what, 70% of cases? And in 20%, to the Rocket Richard winner or a top 3 finisher in Art Ross. And then once every 10 years or so a goalie takes it.
Going back to 1966, the Hart has gone to the leading scorer 34 times in 54 seasons (63%). It went to the runner-up 10 times (19%).
That only leaves ten seasons where the Hart winner wasn't first or second in scoring. Four times, the Art Ross winner missed the playoffs (2002, 2013, 2015, 2018). Twice, the Art Ross winner missed around a quarter of the season (1992, 2000).
The fact that the voters give the Hart to the leading scorer and runner-up so frequently basically takes defensemen out of contention.
In the 1950's and earlier, the Hart voting was way less predictable. (Gordie Howe once lost the Hart trophy in a year where he led the league in goals, assists, and points - that would be inconceivable today). This is probably because the league was small enough that voters could watch a meaningful number of games for each team and make a personal judgment on each player. There wasn't a need to rely on the "narrative consensus" that seems to emerge late in each season. Nowadays, voters have to rely on stats and the opinions of others when there are so many teams and so many games - and, as I noted earlier in the thread, it's easier to measure how a forward is doing, so it's easier to build a good narrative around a forward's season.