When Christians started to evangelize to non-Jews, they adopted pagan holidays as Christian holidays so as to make the conversions easier.They just keep the Jewish culturalism flavor to their lives. I wonder why that even stopped. The first Christians were this way. In the New Testament, it was one of the more hotly debated subjects between James, Peter, and Paul on whether Christians could even be Gentiles. Now it's the other way around.
If you think about it, "Jews for Jesus" is the same approach. Keep the old traditions, just add Jesus into the mix.