I think the answer may boil down to greed and consumerism. Every now and then we hear that America is the greatest consumer nation in the history of the world. This means that most Americans believe that buying or getting more material goods will bring them happiness. As you can see, most people are still unhappy no matter how much money they earn or spend.
I believe this problem of believing money and material goods will make one happy results in America having more money problems than other countries. As everyone joins in the relentless pursuit of money, people start getting competitive and their ego then depends on who makes the most money. This results in the banks expansion of risky credit to make more profits, which results in more money in circulation which results in more greed among the populace.
I do not believe Americans are the only ones with money problems as the capitalist model has been exported all over the world. Europe, China, Russia and India, indeed I believe the world is now having money trouble.
Perhaps the best way to combat the worries and stress of money troubles is to realize you can't really bring all your money to you to your grave, so as long as you have some food and shelter, just live a happy life :)
Hope this helps.