Why Hashem never send prophets for seemingly more obvious issue, like the fact that pretty much every other nation outside israel worshiped different gods.
If Hashem is God of all, the Niniveh citizen were guilty of something far worse than robbery. They worshiped the wrong elohim.
Yet throughout the tanach, I have never seen Hashem make an issue with non jews worshiping other gods. It was as is those other gods are indeed the proper gods to worship among non jews. He seems to only be concerned with jews ended up worshiping those other gods too.
http://biblehub.com/micah/4-5.htm for example says:
For all the peoples walk every one in the name of his god; and we will walk in the name of Hashem our God for ever and ever.
If Hashem is only the god for the jews, why bother sending prophet to Niniveh? They're non jews anyway. Why care about them? Don't they have their own gods?
If Hashem is god of all, why not tell pretty much every single nation at that time that they're worshiping the wrong god? Why worry so much about sodom full of violent, or niniveh full with robbery if they are all guilty of a bigger sin of worshiping idols?