Firstly, that passage only says that 2 workers were of Jewish ethnicity. No news about the congregation.
Second do remember that Christianity was still a Jewish sect and considered as such right until the Kitos war. The followers of the way met in synagogues.
Jewish people didn’t “leave” anything. It was like different views within a current church. These were Gentile and Jewish followers of the way, not a separate religion until the 2nd century.
Think of it as the methodists leaving the Anglicans. The methodists were still Anglicans meeting in church of England churches until gradually they weren’t.
I think that's a nice way to put it but the reality was much different.
First of all Christians were persecuted tremendously. The bible record shows that the Jewish establishment did not like Christians. They were going against the orthodoxy of the church. They didn't fit it. They were radicals. That's the main reason there weren't many Jewish Christians left.
Later though it became worse. Rome ruled Judea at the time of Jesus and beyond. Judea had a series of violent rebellions against Rome. Even in times of non-active rebellion Jewish fanatics, zealots, were actively working against Rome and many times assassinating Jewish collaborators and Roman officials. This of course came to a head in 70 AD with the sacking of Jerusalem by Rome and the destruction of the temple.
After this it became increasingly difficult to identify as jewish in the Roman empire. You were an object of scorn and hatred. These are the roots of anti-semitism.
You are correct though that in the eyes of Rome Christians didn't SEEM that much different than Jewish people. They kept the same holy days. They refused to eat animals that God said not to eat.
So what happened is that the timid Christians stopped keeping the holy days. They started eating pork and what not. In other words they changed their religion to become more acceptable to Rome...to avoid persecution. THESE are the roots of modern Christianity.
In other words modern Christianity is the result of those who wanted to avoid persecution and so avoided looking Jewish as much as they could. They ended up observing pagan days that were acceptable...dressed up of course as "christian" days...instead of observing the days that God set forth as HIS days in scripture.