Do you really believe teamwork will work that easily?
Let's use donations and charities, for example. Some of them are people who have cancer, but there's just little amount they receive from people. Those human beings are dying, and yet the donations are very low.
Now, let's change the subject to the "debt" of the USA. Do you really believe that non-Americans will just easily give out their money for their own debt? I doubt that. Heck, even some people of them might not help out, especially those who don't trust their government.
Also, there's no assurance that those commodities will increase in value once it is paid.
As people have different interests and mindsets, it's very difficult for them to work together with varying levels of trust. So, the question that arises is: Is it easy to manage teamwork? But the actual concern is to create a system where every individual has some reasons to run the system instead of cooperating with other members. I can justify it by example. For instance, in charity, people have the mindset that, with a small amount, a huge impact can be created, and this system actually doesn't give any personal benefits to donors, but in reality, they become a part of this system through their intentions and willingness to give help to needy people, and your example of Cancer patients really justifies.
In this sense, a question is raised: Why would non-Americans be willing to use their money without any personal benefits and trust? Here the accurate answer is the government. When the government gives benefits in any sense with complete transparency, then people agree to become a part of this system; otherwise, people always try to avoid becoming a part of this system that works on the principle of cooperation beneficial for everyone.