/u/talondearg answered that in a previous thread.

Judaism

One of Judaism’s main advantages when it came to relations with Rome was that it was a religion with a homeland, an ethnos, and a long pedigree. Antiquity, not novelty, was respected, and the Jews had it in spades. This, alongside their rather stubborn monotheism, secured them a ‘place’ in Roman civic life, but always an uneasy one. While these elements secured a place for Judaism, they didn’t make it likely to sweep the Roman Empire. Judaism was closely tied to a land and an ethnic people, and they were not, on the whole, very active in proselytising. To become a Jew, besides circumcision for males, was a major step that reconfigured your whole social identity and role.

And, given the Jewish Wars, the destruction of the temple, and the razing of Jerusalem, later Jew-Roman relations were even more tenuous. Messianic Judaism’s great dream was of a Jewish Kingdom, not to take over the Roman one. With the events of the late 1st and early 2nd century, the only real alternative to Christianity, within a Jewish sphere, would be the development of Rabinnic Judaism, which showed no movement towards active conversionism.