Some 2 percent of the Arabs of the West Bank and Gaza are Christians. Not so long ago they were roughly 15 percent of the Arab population. The rest are Muslims, all Sunnis. What explains the decline? Birth rates, of course. Christians are better educated than Muslims (all over the Middle East), and they know that if you want to raise a productive, truly loving, and educated family, you'd be wise to raise fewer children and give them all more attention.
The other reason that so many Christians have gradually abandoned Palestine is that their living among Muslims was a frightful experience. (Christians began decades back in deserting Iraq, too--at least, those who were not slaughtered.) Now, many Christian clergy have lined up against Israel, because they know that the Jews will not harm them. Moreover, they don't want to and have no reason to. The Christian authorities in the territories (and in Jerusalem) try to pacify the Muslims by joining the ugly chorus against Israel. Although they have been playing this appeasement game for nearly a century, it has done them no good.
My own response to this is here.