They don't need to provide a reason, its probably related to greed etc, but greed is still a rational reason. Iran attacking their neighbors is not rational here, it just makes the middle east hate them more.

I am not talking about international laws here, just the norms everyone follows in wars. Everyone breaks the international laws, but the norms of not attacking third parties etc are there for rational reasons, since you don't gain anything for doing so its just stupid and causes damage and strife and hurts you for doing it.