Well, I think it has a bit to do with the history of the usage. It used to be just "Christian". People talked about Christian history, and Christian values, and Christian morality, and Christian tradition. If you look at the Google ngram viewer, "Judeo-Christian" doesn't even register until 1933, and gradually picked up popularity through time. Basically, it was a way to often be historically correct as well as inclusive of the history of the Bible, to add "Judeo-" before "Christian" in certain circumstances. The Old Testament is Jewish, so referring to values, traditions, and history of both Old and New Testament as Christian leaves out the Jewish aspects of it. Some continue to say "Christian," while others have modified the term with "Judeo-". It's less of a modification than using the completely different word of "Abrahamic". But "Abrahamic" isn't necessarily the correct term, anyway. Typically, when the words are used, they are genuinely talking about only Jewish and Christian issues, not Muslim. Abrahamic refers to Jewish, Christian, and Muslim, so should be used when talking about all 3, not when talking about a tradition that doesn't include Islam, for example. In any case, if you look at google ngram viewer, Abrahamic has a longer history than Judeo-Christian. For some reason, Abrahamic starts being used a lot in 1828, and has gradual spikes in popularity followed by no use. But around 1965, it started to grow in popularity in English, and its usage continues to rise, though has not reached the heights in usage of Judeo-Christian (in English).