"And what did Hamas do with Gaza when Israel withdrew in 2005? Build factories, employ Palestinians, grow olives, grow tourism?"
Is this what you call "withdrew"
Israel controls the Gaza Strip's northern borders, as well as its territorial waters and airspace. Egypt controls Gaza Strip's southern border, under an agreement between it and Israel.[59] Neither Israel or Egypt permits free travel from Gaza as both borders are heavily militarily fortified. - https://en.wikipedia.org/wiki/Gaza_Strip
The port has been bombed. So too the water treatment facilities, the sewage treatment, the hospitals... the power generation. There's no end to the criminality of the Israeli government.
There are no roads in or out, except what Israel allows. Produce is allowed to rot at checkpoint. Fishermen aren't allowed to access the sea.
As one scholar put it, it's "the quiet suffocation of two million people, offered only two options: either to die screaming in war or die silently under siege." (Khaled al -Hroub - professor of Middle Eastern Studies, Northwestern University in Qatar and author of two books on Hamas)