I read this as another group, not a nation state, wanting and stealing the ammonium nitrate. Most of it was stolen before the blast — terrorist groups? Low-level thugs? Who knows, but you’re right that a nation state doesn’t need to steal it in this way. That’s why it points to other parties.
It may be incredibly common but not in the quantity that was stolen.
Must take in mind that the stuff also decomposes spontaneously. If stored for many months in bad conditions of conservation some amount just would go silently to the air in form of water vapor and laughing gas.
It may be incredibly common but not in the quantity that was stolen.