They already lived through 4 years of Trump and have decided it is worth doing it again instead of letting the party most currently responsible for said genocide to win.
Point being that Harris has outright refused to meet any sort of demands on Israel. There was no reduction in arms nor any restrictions placed on Israel, and Harris fully intends to continue that policy.
If she loses, it means that she failed to meet her constituents demands, which means they'd have to actually meet them in the next election to win.
Also because I have a hard time seeing how anyone who lost entire family trees would listen to "uM AkShuLly TrUmP woUld bE 9999x WorSe, wE jUst NeEd tO ProTest aFTER tHe ELeCTion" as if we didn't just full send billions of dollars in munitions and weapons to Israel.