Why are there still poor people in America half a century after the implementation of a system of social welfare programs that were designed to...

The way a person answers this question depends largely on
their political ideology.  Therefore, there are many possible
answers.

A conservative might argue that poverty persists
precisely because of those programs.  Such a person would
say that welfare programs have encouraged poor people to develop bad habits in which
they rely on the government for help.  The poor would be better off if they would be
made to find work and develop the habits that lead to
success.

A liberal might argue that poverty persists
because the social programs you mentioned have been too limited or have not been done in
the right way.  Such a person would argue that our government does not do enough to help
poor people obtain child care so they can work, or get job training so they can find a
good job.  Such a person might argue that the government has not done enough to help
poor children get a better education.

So, depending on
one's political ideology, one can attribute the persistence of poverty to excessive
government action or to lack of government action.