I think the black demographic doesn't have much interest in Hockey due to it being a primarily white sport. Lack of representation probably has a major effect on the black demographic's interest, that can be responsible for probably at least 1x of that missing viewership I would imagine. Whereas with the NBA they have a lot of interest there with their over representation in that sport, and the sport generally being more relateable.
Black guy here. We don't have much interest because...
1) the NHL has never made much of a concerted effort to market itself or make itself more appealing to demographics outside of its primary audience;
2) the game is a niche sport and has no foundation at the grassroots level in places where the demographics aren't primarily the homogeneous and monolithic ones it already appeals to;
3) the expense of the sport and lack of subsidized initiatives to introduce kids to the sport at a young age means people gravitate towards the more easily accessible options instead (and that goes for all demographics and is the primary reason why the NHL's talent pool is so small);
4) Hockey's representation is minimal because its athletes are generally not marketed due to more importance being placed on the NHL projecting a particular image rather than letting the individuality of its athletes become marketable. And the game itself is more interested in maintaining its traditional aspects than finding ways of improving its product and appealing to a more diverse audience;
5) Non traditional demographics who do try to get into the sport at the grassroots level are either subjected with being reminded constantly they're outsiders in this game by vitriolic parents and peers and fans. And those who come to it as adults are constantly told by a large contingent of insecure hockey fans that the sports they already enjoy are "dumb, stupid and boring" while only harboring criminals and appealing to the lowest common denominator. Not very welcoming.