Doesn't matter where you're from, you are spot on with surgical precision about what hockey is, what hockey gaming is, what hockey gaming was, and what is sorely lacking in today's video game. I turn on Legacy every now and then (and it helps with up to date rosters) I play a game and I marvel at the realism in the gameplay. I may very well just play my season with Legacy this year for that very reason. Even NHL09 on PC one of my absolute favourites just gets hockey so right. No game is perfect, but those two do far more right than wrong.
To answer your question, it is purely turnover and market penetration. There are simply not enough people that play NHL as there are that play FIFA and it comes down to popularity of the sport but it would be wrong to not acknowledge the popularity of the respective game series'. NHL the video game's popularity was largely, if not entirely, founded on and created by the popularity and ubiquitous nature of the Genesis years specifically from 93-97 when people who didn't even like sports found themselves playing NHL. In North America that had an enormous popular culture influence and a massive influence on how all sports games were developed from that point on. Even FIFA's first 3/4 angle was a variation on the usual look of the football pitch from previous years (mostly up and down or side to side) which was aided by looking at NHL and saying, "well, that non-side to side view of the rink worked well, how about an angled look of a football pitch to show you more of what's going on." It worked so well, they did it with the early NBA games as well.
My point is, I would argue that part of what makes FIFA more popular today is that what once made NHL so popular has since faded as the generation that played the 90s NHL has aged and perhaps left gaming or only continued playing the older game. FIFA on the other hand has developed over time. I would say that it's truly global appeal didn't really hit its stride until football from around the world started becoming more watched around the world and where local brands and jerseys weren't only familiar to people of that region. So, one could argue FIFA became the juggernaut it is today sometime at the end of the PS2/XBOX era when both itself and PES had to do different covers for different regions with different athletes. That doesn't happen anymore for anything other than special edition covers. Mbappe gets a cover all over the world, it doesn't change to a more local star when you're in Argentina or Japan or Canada.
On last exploration of sales, I remember seeing NHL selling vaguely just under 1 million copies per year, all consoles combined. FIFA sells several times that. It's as simple as that. There are parts of the world that simply have no cultural reference for getting into ice hockey. Just like most North Americans have absolutely no connection to pro cricket and pro rugby.