Back in 1949, there wasn't much of a difference between Jordanians and Palestinians - they'd been administered separately during the Mandate and prior to that were in different provinces, but they weren't separate peoples. But that's several generations ago, by now they definitely are separate... neither the Palestinians nor Jordan would want that. Especially since, as someone mentioned elsewhere in this thread, Jordan has had bad experiences with the PLO trying to take over their country, so they won't be too keen to go back to the pre-1967 situation and take on a large number of additional Palestinians.

As for Egypt, they were a separate country from the Levant for most of their history even if there were also periods that they did control it, so definitely different nations. And modern day Egypt already struggles with discontent and Islamist resistance in Sinai as it is, besides all their more general problems, it's quite understandable they wouldn't want to add another restless province on the far side of Sinai, even if the Gazans wanted that.