Partly size, mostly history. The association founded in Mikao Usui's time still exists, but its Tokyo headquarters was bombed in the Second World War and the people inside were killed, and after the war it dwindled. Western-style Reiki came back to Japan in the 1980s and 90s, and interest in the traditional practice has been growing slowly since the 2000s, but the association itself is still small and elderly.

Traditionally, no. The system of Reiki has three levels: Shoden, Okuden and Shinpiden. Some Western forms split the third level into a Level 3 and a Level 4, and the Japanese association has at times divided Shoden and Okuden into sub-levels, but there is no Level 4 as such.