In the end of the day, it's the law of the strongest. It's no accident that Israel hoard a lot of weapons of war and build defensive systems like the Iron Dome. It's a show of power for a very simple goal: deterrence. I don't think Israel really though of using all their weapons, but just having them makes every one the enemy nations that surround them to think twice before attacking them. Well, Hamas did not think twice. And they cannot say they didn't saw it coming.
Israel accepting a ceasefire deal would be nice for saving lives and all, but would leave them vulnerable for future missile attacks from Hamas. A nation will always think of its own citizens first. Maybe the Hamas already counted with this reaction of Israel, and though that other Arab countries would form a coalition to fight Israel simultaneously. Well, it didn't pan out. Deterrence worked after all.