not sure there is a principled reason why the power to govern the exchange of goods and services (which is what money facilitates) should be up to them.
Except in some theocraties where you're 2nd class citizen when you don't worship the official God (Israel, some Muslims countries...)
And in the US, the President oauth is on the Bible and "under God" if I remember clearly. So, in a way, it is still the case: how would a Jew or Muslim or Buddhist be able to do that?
Governements are elected to provide services for the good of the nations. That include security: physically (police, army) and economically... so the money is a way for a state to provide security for the trade
Federal public officials in the US can swear on anything they want to, the Bible is not a requirement.
That really needs a standardized currency.
assumption right there