This was not uncommon for the Jews. The ten southern tribes had gone into captivity in 722 B.C., and Judah went in 586 B.C. The temple that they had been worshiping at was built by Herod, and it was not that old (comparatively). The Jews were used to being in captivity and used to being scattered.Pointing out is not proving. Shall I go through a long list of quotes showing how the Jews permanently had their power structure destroyed? I direct your attention to Ussher, whose Annals is a compendium of several ancient sources. After the period of 70 - 73 the Jews no longer had wind in their sails. They were in no position to Judaize.
Furthermore in the time of Christ they came from all over for the feast of Pentecost. It doesn't seem like many of them lived right in Jerusalem.
And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. (Acts 2:5)
And how hear we every man in our own tongue, wherein we were born? Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia, Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes, Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God. (Acts 2:8-11)
It seemed as if these Jews came from every part of the known world. They had not all gathered to live in Jerusalem. Very few actually lived in Jerusalem. Antioch may have been a larger city than Jerusalem.
Insomuch that they brought forth the sick into the streets, and laid them on beds and couches, that at the least the shadow of Peter passing by might overshadow some of them. There came also a multitude out of the cities round about unto Jerusalem, bringing sick folks, and them which were vexed with unclean spirits: and they were healed every one. (Acts 5:15-16)
--Peter demonstrated the gift of healing here. It wasn't so much the sick of Jerusalem that came to be healed here, but rather those from the cities round about unto Jerusalem that came to be healed. One needs to study this passage carefully. For when Titus destroyed the Temple in 70 A.D., yes, Jerusalem was destroyed, but what about the cities round about Jerusalem that Peter is referring? Were they also destroyed. That seems to be where most of the believers were.
Judaizers exist today in their many forms. If you want some examples look at the Church of Christ, and even in the RCC. In its strictest form there are still those that require circumcision as a part of the gospel. To say that these false teachers ended their false teaching pre-70 A.D. is quite a stretch of the imagination. We will always have their false teaching just as we will always have one of the earliest of the heresies to enter Christendom--baptismal regeneration. It came early and is still common today. Heresy just doesn't fade away. It reappears. Sometimes in different forms but it never simply goes away. There is nothing new under the sun.