I hate to say it, but the reason people don't watch the NHL is simply because it's very boring.
There is nothing wrong with the game of hockey itself, however there is no question that the NHL is run by people who can't match the product that the NBA, NFL and MLB create. The reason why marketing of NHL and it's "star" players won't work is simple.
Outside of the ice they are very bland and boring people. Pretty much all of them come from upperclass neighborhoods, the worst tragedy that has happened to them is when their supreme backpack got stolen in school. Generation Z cares more about the players and their stories than the actual teams. Guys like Mcdavid and Matthews have zero charisma about them it's literally impossible for the NHL to market them.