To use my own religion as a preface, no versions of Judiasm actively seek to convert anyone for any reason. The option is available if people feel like they might want to convert, but depending on the version of Judaism you're dealing with the prospective convert may have to study for a year or more and then go before a panel of rabbis who will then judge if that person is ready to convert. There is no incentive or motivation built into the religion which would encourage its members to go out into the world at large seeking to convert non-Jews. Its members simply believe in what they believe in, and to them the rest of the world can make up its own mind.

Certain versions of Christianity encourage their followers to believe their souls and the souls of others are in need of saving. Certain versions of Christianity encourage their followers to believe that by saving souls of other people, their own soul will more likely be saved. How might one go about saving someone else's soul? But of course, by converting them to whichever version of Christianity they happen to believe in. Therefore, because certain versions of Christianity encourage their followers to actively seek out people that are not followers of their particular version of Christianity for purposes of saving a buncha souls, those versions of Christianity engage in self propagation through indoctrination.