It is an interesting article from Wikimedia blog (I didn't know that wikipedia did such interesting studies! that talks about popolarity of Olympic athletes in different countries:
But the old saying big in Japan did not apply to Phelps, where he placed 12th, the only place where Bolt was more popular, by about 25%. To be big in Japan, though, you really had to be Japanese. The top seven Olympic-related articles were filled by Japanese medalists, not even interrupted by general articles like 2016 Summer Olympics or All-time Olympic Games medal table which were usually popular across the board. Japans list was led by Saori Yoshida, who won wrestling silver, and had 240% the views of Phelps. She was followed by many others, presumably now household names in Japan, including gymnast K?hei Uchimura (#2) and table tennis whiz Ai Fukuhara (#3).
I think the Japanese swimmers like Hagino stole the attention of swimming fans, and the general fan had Yoshida, Uchimura, and Ai-chan. Bolt had more attention because there was no competing player from Japan in the short distance track events (the success of the relay team was quite unexpected), and well, he is the fastest man on Earth!