Guidance
Muslims are not required to actively recruit others to Islam. In the Qur'an, Allah told Muhammad that "You certainly cannot guide whomever you please; It is Allah who guides whom He will. He best knows those who accept guidance." (28:56). Muslims are expected to explain Islam to followers of other faiths, but it is up to Allah to guide those whom he wishes to.
http://www.religioustolerance.org/isl_intr1.htm
So...why doesn't Allah swt guide everyone? :S