God didn't give the Jews a super weapon because he was the super weapon.
The covenant with the Jews is that if the Jews keep the Torah, God will protect them. If God gives them all machine guns with unlimited ammo, they don't need God to protect them because they could just massacre all of the Canaanites, Philistines, Arameans, Assyrians, Babylonians, and Egyptians within a month.
God wants the Jews to be dependent on Him so they will always serve him.