Two reasons:
First, as I said above, There is reason for Arab nations not accepting Palestinians. It is exemplified by the experience of Kuwait.
Palestinian communities allowed entry go to work to take over the nation that accepts them. They act as a separate ethnic group intent on domination, and do not integrate into the nation that accepts them. This is as true in Lebanon and Egypt as it was in Kuwait. The relations inside Jordan with Palestinians are uneasy.
This is visible in the United States Palestinian communities as well. They are the leaders of the anti-semitic hatred and calls to war in the USA. There is little difference between the Palestinian's relationship to Israel and Palestinian's relationship to every other Arab nation.
Second, the Palestinians have become a pawn, mostly a pawn of Iran, but also a pawn used by the rest of the Arab world. The Islamic world is mostly a world of dictatorship, whether the nation's leaders are called royalty or dictator or president. The two most democratic nations are Syria and Iran. However, Iran is not Arab, it is Persian, and Iran has a deep history of conquest. Iran is the only Shia nation in the world. Shia are the result of the Sunni-Shia schism after the death of Mohammed.
When Mohammed died, his top generals that surrounded him slaughtered every relative and favorite that Mohammed had in his life. The evidence suggests strongly that those men hated Mohammed, and did not believe in his war cult --- that they wanted to destroy it. But, after successfully taking over, they apparently decided to keep the machine of islam going for their own benefit.
Shia are the other side of that slaughter by the generals who became founders of Sunni islam. Shia are followers of Ali. Ali was the last heir to Mohammed's legacy, and he was killed in the great mosque of Kufa in Iraq. Consequently, Shia do not recognize any Kalifa (Caliph) as legitimate, because the last heir was murdered and heretics claimed the throne. So Shia are ruled by councils of Imams. This makes them prone to democracy. It may be a cultural reason for the cycle of harj-o-marj in Iran.
All of these governments benefit from the Palestinians being forged into a cannon-fodder army culture. Directed against Israel, with control maintained by systematically murdering all Palestinians that dissent or seek peace, the Palestinians are a PR tool. Their "oppression" allows the rulers of the Arab world to direct the disgruntlement of their own peoples against Israel and Jews. And this is not new at all.
This strategy of use of Jews as the bogeyman had its inception in economics, and the history of the islamic empires across the Middle East and Africa. The fundamental economic problem within islam is that muslims cannot be taxed. (The secondary problem is that interest could not be charged on loans.)
So after a region is conquered, and most people choose to convert, this leaves the dictator (Sultan or Caliph) with a big problem. The spoils of war will run out, and if you cannot continue to expand your empire, which has an endless need for new slaves, more gold and silver, and more land as spoils of war --- how are you going to fund your nation? The answer was found in the Jews --- that dedicated minority of Jews that refused to convert and survived.
The solution was to favor Jews as merchants (and money-lenders). Jews also became favored sometimes as advisers, and one Jew became a famous general, second only to the Sultan. Jews were safe, because they could not ascend to the throne. And those who got close to the throne depended upon the dictator for survival. So their loyalty was guaranteed.
By favoring Jews to be the biggest merchants the rulers could charge the Jews any amount of tax they wanted to. This acted like a VAT system. They also came to favor Jews as civil servants for the same reason that Jews could be trusted advisers and even military leaders. A side effect that was very desirable for the leadership was that this directed the anger at the extreme inequality in society at Jews rather than the ruler himself.
In Spain, Moors saw fit to do something very anti-islam. They made it illegal for Christians and Jews to convert to Islam without invitation. This was an economic decision. It allowed the Umayyads to collect taxes on the people of Spain at a level that supported their empire. Without this, the Umayyads probably would have fallen. In Spain, Jews were the civil servants, the faces that Christians saw. This directed the hatred of Spain's Christians against the Jews. And it also laid the foundations for the rebellion that took back Spain for Christianity. It laid the cultural foundation for the Inquisition.
The Spanish Inquisition was not just about hatred of Jews, although the cultural history helped make it work. The crown was in trouble, because although banking had been invented, reserves were gold and silver, and the money-multiplier of banking was at its limits. Confiscating the property of wealthy Jews shored up the finances of the Spanish economy. Spain also sent out desperate expeditions to get more gold, as most people know.