I would argue that's true of any and all sports
Like tell me a sport that is number one in a country that wasn't 10, 20, 30, 40 or 50+ years ago? Sporting culture in all countries seems to be deeply ingrained and other sports, regardless of how popular they are elsewhere make very little headway in the market. Even Soccer, as ubiquitous as it is in society, fails to overtake the traditionally popular sports in markets like the USA, China and the old commonwealth countries.
In Australia, I would describe rugby league, AFL and Cricket as the tier 1 sports in terms of overall popularity and that has been the case, as far as I can tell for over 100 years. I don't ever see that changing.
That's not to say sports shouldn't try to get a slice of the pie, especially in the American market and if the NRL makes some money on it and develops a sustainable niche market then it will be a success.