It has been long since Judo was not seen as an entity exclusive to Japan anymore
Why does Japan lose in the Olympics and other major international competitions? Is it because of the hovering Japanese judo world? Or is it from the lack of dominance that Japanese athletes have in judo as a sport? Although various theories exist, the fact is that in Japan, judo lies in another plane apart from other sports because it is considered as the country's speciality.

What is a country's "speciality" in the first place?

Is ice skating Russia's speciality? Is table tennis China's speciality? Is boxing Thailand's speciality? Finally, are Sumo and Kendo Japan's speciality? Do Chinese people consider Kung Fu as their speciality and/or a type of sport?

Yes, it is true that Judo is more familiar to Japanese citizens compared to other countries, since dojos(training halls) are nearby, and most schools have either a judo team or a club. However, just because Judo is Japan's speciality, is it appropriate to believe that Japanese judoists must have an advantage, and that it is no surprise for them to win in international competitions?
Many other countries have the environment necessary to develop one's talent as a Judoist, and Japanese athletes do not seem have an advantage over foreigners in terms of physical characteristics.

Judo in Japan has also changed
The tactics have changed from competing in the flow of continuous judo moves to judging each move by move. This changing trend inhibits the growth of judo as a martial arts.
Even in Japan, judo is promoted only as a sports; not martial arts.
Why is Judo a global sports while Kendo and Kyudo(Japanese fencing and archery, respectively) isn't?
Since when did Judo become an international sport and foreign athletes increase their power?

Anton Geesink, who stands on top of the amateur sports world as an IOC member, holds the key to this.

Out of all the different sports, it is very rare for a former athlete to hold the position as an IOC member. The fact that judo, 'the' martial arts of Japan, created a man of power called an IOC member is a major part of the history of modern judo.
Yet, the fact that Geesink acquired the gold medal in the Tokyo Olympics is even more significant, for it was such an epoch making event in the history of modern Judo.
The Epoch Making Event
Judo was first introduced to the Olympics at the Tokyo games in 1964 as a one time event. However, with the gold medal won by Geesink in the Men's Openweight(victory by an athlete from the West), judo became an official event.