oh boy. since this seems like a genuine question, I'll answer it.
first off the answer is, they do. all of the major refugee camps outside Gaza/WB are in Lebanon, Jordan, and Syria. as tea said, they make up 10% of the population of Lebanon. They're more than 1/6 the population of Jordan.
they're also worried about their domestic situations. Jordan literally fought a short war - Black September in 1970 - to prevent Palestinian militants from taking over Jordan and expelled them to Lebanon. that in turn was a major cause of the disastrous 1975-90 civil war in Lebanon. during that civil war, Israel invaded in 1982, expelling the PLO from Lebanon (as well as directly causing the formation of Hezballah, and getting the IDF stuck in a frutiless 15-year occupation of Lebanon).
Palestinians are, unfortunately, more useful to other govts as a symbol than as potentially destabilizing residents
the historical treatment of Palestinians by Arab govts is shameful and at the same time doesn't justify any of the bad things Israel's has done