Why did the Articles of Confederation fail?

They failed because they did not manage to convince the
elites of society that their interests would be protected by the sorts of governments
that sprang up under the Articles.

During the time that the
US was under the Articles, there were various kinds of economic problems.  The state
governments' responses to the problems (spurred by the demands of the common people who
were being hurt most by the problems) hurt the interests of the elites.  They also
convinced the elites that the nation would not be able to prosper economically under the
sorts of governments that would take those steps.  (Follow the link to see what the
economic problems and the states' responses to those problems
were.)

So, the Articles failed because the elites who took
the most interest in government felt that the governments were acting in ways that were
bad for A) the interests of the elites and B) the long-term interests of the country as
a whole.