The explanation is simple: Judaism does not proselytize and conversions are difficult. Christianity and Islam on the other hand actively seek to convert as many followers as possible.

While the three "Abrahamic" religions share a common descent, Judaism is significantly different, since the religion is closely tied to an ethnicity, and a large part of the identity is the shared heritage and history of the Jewish people. Therefore Judaism only grows through demographic changes. Christianity and Islam on the other hand are not tied to any specific ethnicity or nationality, and have grown through various means like conquest, mass conversions, mission work and so on.