You would not have to ask why if you knew the history of the area a little better. You are probably thinking why did Israel get so aggressive after 1200 Israelis were massacred and hundreds of hostages of all age were brought back to Gaza?
The periodic removal of Jews from Gaza goes back at least to the Romans in 61 CE, followed much later by the Crusaders, Napoleon, the Ottoman Turks, the British and the contemporary Egyptians, and more recently Jews removed themselves from Gaza in 2005 and it appeased no one. Within a few weeks of every last Jew removing themselves from Gaza, Hamas rockets rained down on Israel. Lesson learned! However, Jews definitely lived in Gaza throughout the centuries, with a stronger presence in the nineteenth and early twentieth centuries. How many live there now?