One way to explain this is to say that part of Christianity is an emphasis on personal responsibility.
It is, of course, true that many Americans are poor. But this does not necessarily imply that the rest of America is not truly Christian. Christians are called to help those who are poorer than them. But this does not mean that they are called to simply give the poor money. If we were to create a comprehensive welfare state that eliminated poverty (if this were even possible), we might arguably be hurting the poor. We would be rewarding them for bad behavior. By this argument, the poor are poor because they have bad habits and do not do the things that would get them out of poverty. The best thing to do, then, is to hold them responsible for what they do.
If we hold to this point of view, we take a more expansive vision of what it means to help the poor. This point of view holds that we help the poor by requiring them to be responsible for themselves, not by giving them handouts that encourage them to become and remain dependent upon others.