Billiards is not the recognised national sport for any country.
Japan is the birth nation of this ancient martial art Karate, which is one of the most popular sports in the world.
Rugby is not the national sport of any country in law, but it is considered to be the national sport, 'de facto', of Wales and New Zealand.
No, there are no more issue than with karate then any other sport.
The most common sports in Japan include association football and other ball sports. Some of the martial arts and Karate are also practiced by many people. There is no legally official sport of Japan, but the Japan Sumo Association describes sumo as the national sport of Japan, with baseball as the most popular spectator sport of the country.
I don't think you can pin the blame on that to any one person. There are many styles that continue to stay away from the idea of competing in karate as a sport.
they don't have any
China doesn't have any national sport. However, table tennis or ping pong is a famous sport from the olden days of China.
The University of Oklahoma did not win any national championships in 2010. The last time a sport at the university won a national championship was the 2008 gymnastics team.
Greensleeves is not the national anthem of any country.
It would be hard to specify one single national interest. Like any country, Ireland has many things of national interest. Music, culture, sport (namely our national sports of Gaelic Football and Hurling), news and current affairs, weather, agriculture, history and so on. It would be much the same as any country.