Do you suppose they gave up their land and livelihoods voluntarily, in order to go and live in a refugee camp in Syria or Jordan? Do you imagine they had a choice?
No, they certainly didn't, but many of the expulsions at that time were brought about by the Palestinians own youth who were rounded up and taken to Bulgaria and Russia to be 'indoctrinated' and who came back as ruthless terrorists to intimidate and murder their own people who were happy to live along side the Israelis, this didn't suit Russia's plan for de stabilizing the Middle East. Other expulsions were brought about by absentee landlords selling their rented out land and properties to Israelis without any consideration for sitting tenants. And yes, the Israelis were responsible for some expulsions too.
Winston Churchill was a brilliant man but the idea that you could reintegrate the Jewish people that survived back into the Soviet block of countries and Germany in the immediate post war period was just fanciful.