It's all about psychology and the lack of confidence
con·fi·dence /ˈkɒnfɪdəns/ Pronunciation Key - Show Spelled Pronunciation[kon-fi-duhns]
–noun
1. full trust; belief in the powers, trustworthiness, or reliability of a person or thing:
Trust is something that is built over time, in repeated interactions between individuals. You trust McDonald's will make you a Big Mac a certain way, you have confidence in their ability to provide that.
Trust is something that can be gradually eroded or can be destroyed rapidly. If McDonald's started making crappier BigMacs with less meat or something, you would gradually trust them less - or come to trust that what they were making was no longer good.
Trust is something that also can be wiped out very quickly, (i.e. a number of e. coli outbreaks in the food industry). That lack of trust spreads quickly and would be difficult to rebuild.
You trust that the paper in your wallet can buy something tomorrow because someone else will trust that they can buy something with it too. It has no foundation, eventually will be sufficiently abused until the trust is gone. The Romans debased their currency too by mixing other metal with silver to fund their wars, they just did it over hundreds of years.
If the rest of the world lost trust in the dollar today it would collapse in hours if not minutes.
Americans' psychology has nothing to do with it because Americans don't realize that their trust is falsely placed.
I'm a shrink, I deal with trust and psychology everyday.