

The problem is the other side:
The seller has a huge interest to not deal with too much fiat exchange. There’s always fees and market risks associated.
The USD historically was very stable compared to the rest. That in combination with the huge purchasing and military power the US represented while being reliable as a trading partner pushed the US dollar into focus.
The USA then spent a lot of time, energy, money and lifes (mostly others) in ensuring this dominance.
Think of it like a language: a Spanish and a German work together in English - not because it’s impossible for them to learn each others language but because the overhead is too big.
Specifically to your example: no one wants to sell anything to Russia in rubles.
Imagine this scenario:
Hey, I’ll pay you 100 YC (your currency).
Oh since we agreed on the price a few days ago it’s only worth 80YC.
Oh now it’s 120 YC but no one else will take the currency I’m paying you in except me.
Oh now it’s worth 10 YC but we signed the contract, hurray!!


Can’t tell you about the first half of your question as I’m not familiar with the American doctrine.
And before someone jumps into discussions: I’m relying knowledge, not conviction - if you have more insights, please add them. But if you try to convince me that it’s wrong or try to point out inherent inconsistencies: you’ll add nothing for me - preaching to the choir and so on …
the second part is actually straight forward: Jews in the Bible didn’t believe in JC either - by definition.
The reason why the Jewish faith has a special role for Christians lies in the old testament, not the new one: they are “God’s chosen people” and everything resolves around then bring pampered by God, both in the positive sense as the favorite but also in the negative sense as the one’s who receive the stick more.
Speculation part: This unique position is very present to all Christians, but especially the more fundamental ones. Combine this with a history of mistreatment, where jews were blamed for everything that went wrong in your neighborhood and you have a good mix of the enduring, suffering chosen ones.
Note: Israel as state is then a completely different discussion.