At last minute, the BBC has canceled a documentary that claims to show that the exile of a large part of the Land of Israel's Jews by the Romans after the Destruction of the Second Temple and the Bar Kokhba revolt that followed a half-century later never happened.
I imagine this documentary is, in part, probably based on the book The Chosen Few, which convincingly shows that the numbers of Jews decreased because of the new post-Destruction demands for community membership – mostly the demand to send your male children to school.
The schools were costly and, in an agrarian economy had little practical value to parents who were expected to do it. Instead, sending male children to school cost farmers and small artisans their helpers and assistants, and drove up the cost of their businesses, meaning the families had less food, less money and less of the necessities of life if they did it.
Christianity was also monotheistic and it made no similar demands of followers, and as such it had a tremendous draw for poor Jews and what we would call lower middle class or working class Jews.
In other words, most Jews simply faded away, assimillating into local Christian sects or the local pagan population, because the cost of schools – heders, yeshivas, day schools in today's parlance – was too high.