It’s because they won’t camp next to the border of Israel and blather on about the Golan. They’re not taking victimhood seriously if they’re trying to get out of Syria.
A better and more correct question would be why are the “Palestinians” treated as refugees or even considered refugees at all? Never in history have we seen generation after generation of any group still considered to be refugees. Even though I raise the question, I know very well the answer: simply because it is fuelled by hatred of Jews.