Because Israel wasn't inclined to do so on its own. It was not in the inherent character.
Kind of like the white space on a printed page. It tells us what's *not* there.
Would other nations have needed to be told? For Ishmael's descendants, a day without beheadings is like a day without sunshine.
Israel miscalculated Moses' return by one day and went off the rails... by rising up 'to play'.
I believe God ordered their destruction because they practiced human sacrifice, specifically of their children to Baal.