There are a number of reasons why the United States did not want to take many Jewish refugees from Nazi Germany.  Among them were:

• The persecution of Jews started during the Great Depression.  The US was not at all eager to accept immigrants in that sort of an economic situation.
• Opposition to immigration in general.  In the 1920s, the US had drastically reduced immigration.  This anti-immigration attitude continued into the 1930s.
• Anti-semitism.  It cannot be denied that there was a great deal of anti-semitism in the US.  These attitudes influenced the government's approach to the issue.

It must be noted that this reluctance was not as morally bad at the time as it looks today.  Before WWII, no one knew that the Nazis were going to go beyond oppressing Jews and start trying to commit genocide.  It is not as if the US was consciously making a choice to commit these Jews to death.  It was, we must admit, turning its back on them and condemning them (knowingly) to being oppressed, but it did not know that they were likely to be killed.