I don't think anyone has really noticed that the pair category is the least popular.
Even in Japan, where there are so many good skaters, there are few participants in pairs
Japan has issues that many other countries don't - limited rink availability (this applies even to singles skating) and the fact that most males who take up figure skating are of small build (even among a generally short/slim population - I am only 5ft4in and many top male skaters are shorter than me!). There are taller/bigger Japanese men, but they are highly unlikely to take up figure skating. I've always wondered whether the federations should recruit taller boys from ice hockey clubs for pairs and ice dance. But boys often grow in their mid to late teens, so a tall 12-year-old may not grow up to be a tall 20-year-old, and obviously 20 is far too late to switch to pairs skating. This is one of the reasons why Japan has to resort to importing pairs and dance men from overseas.