I don’t want to get into the political or moral issues, but I just want to point out that this is almost a non sequitur. The USA’s dominance is relative to other countries, but the poverty line is intra-USA. The single poorest person in the USA could be richer than everyone outside it and there could still very well be a poverty line - and people below it - in the USA.
"a condition characterized by severe deprivation of basic human needs, including food, safe drinking water, sanitation facilities, health, shelter, education and information. It depends not only on income but also on access to services"
I don't know, if the statistic for the USA is as high as the 13.5% cited by GP, but based on what I read about, and some small amount of personal experience, it is unusually high for such a wealthy, proud nation.
The cost of disposable nappies is not the issue here. Neither is happiness or contentness. It's being the richest country in the world while 13.5% of its population is living below the poverty line, while people are literally dying on the streets due to being neglected by both the government, their neighbours, and a lack of acceptable health care. With the poor staying poor due to no social mobility, access to education, or normal jobs that don't involve having to scrounge the bottom of the barrel looking for e.g. passengers to drive around.