Because Muslim countries considered Palestinians the Gypsies of the Middle East as an unwelcome group of people. Arafat going after Jordon didn't help the Palestinian's case either.
People really need to study their history especially the parts about Arafat the terrorist and how Jordon and the rest of the Muslim countries kicked the PLO toward Israel on a bogus land ownership lie in the hopes Israel and the PLO would wipe each other out.