In my life experience, many Americans tend to be selfish individualists and fail to reciprocate or be concerned about anyone else. For example, a donation barrel at a local hackerspace one recent holiday season was essentially empty. Inequality is also rampant as thousands of homeless people live on highway embankments while millionaires drive past in Ferraris.
In areas without community social ramifications (typically large cities), there's little benefit of helping and minimal risks of not helping others. OTOH, there are bigger risks of not being helpful in rural areas where there might be one general store run by one person and where reputation gossip gets around.