Most of those living in Gaza were there before it had "Hamas HQ" move in; and many also don't have the resources to leave, or a place that will accept them.
NOTE: the current mess in the Middle-East; "Israel-Palestine" has devolved from the 1948 war where the neighboring Islamic/Arab nations tried to eliminate Israel and the Jews. That war failed and many Jews living in much of the Islamic/Arab nations had to flee for their lives. Many to Israel, rest to Europe or USA, etc.
The belligerent(attackers) and losing Islamic/Arab nations refused to accept Palestinian/Islamic/Arab refugees from the former "Palestine", hence the ready made controversy/crisis that has brewed and allowed pretext for later wars since.
Jews living in Arab countries left from 1948 to 1973. Except for European Zionism they would still be there.
I know several Jewish families who prospered in Morocco. They aren't Zionists. Their families had lived in Morocco for hundreds of years.