@Justicar They betrayed a Jew (assuming it even happened), they didn't betray their god. But the Judeo Christian viewpoint is that they were god's chosen people until that point, then Christians became the chosen ones. And some even claim Jews are fake Hebrews and Christians the real Jews.
It's all utterly ridiculous, but that's religion for you.
As for why they keep calling them that, it's because Christianity is Judeo. No one loves Jews and did more for them than Christians.