The point at which nascent Christianity ceased to attract Jewish followers was the point at which Christian arguments were written down and could be examined.
Until then, a clever speaker could weave endless tales and attract through charisma. Once there were authoritative letters circulating explaining rationales and proof texts, no one conversant with the authentic Torah tradition was interested.
Believers and contributors would have to be henceforth found among non-Jews who were susceptible to Greek idioms and philosophical methods.
It was true then and it’s still true now.