To avoid the creation of an aristocratic class.

The founding fathers had this specific aim in mind. Details here:

http://budiansky.blogspot.com/2010/10/adam-smith-thomas-jeff...

A relevant quote from the article:

  [Thomas] Jefferson cited Adam Smith, the hero of free market
  capitalists everywhere, as the source of his conviction that (as
  Smith wrote, and Jefferson closely echoed in his own words), "A
  power to dispose of estates for ever is manifestly absurd. The
  earth and the fulness of it belongs to every generation, and the
  preceding one can have no right to bind it up from posterity. Such
  extension of property is quite unnatural." Smith said: "There is
  no point more difficult to account for than the right we conceive
  men to have to dispose of their goods after death."

  The states left no doubt that in taking this step they were giving
  expression to a basic and widely shared philosophical belief that
  equality of citizenship was impossible in a nation where
  inequality of wealth remained the rule. North Carolina's 1784
  statute explained that by keeping large estates together for
  succeeding generations, the old system had served "only to raise
  the wealth and importance of particular families and individuals,
  giving them an unequal and undue influence in a republic" and
  promoting "contention and injustice." Abolishing aristocratic
  forms of inheritance would by contrast "tend to promote that
  equality of property which is of the spirit and principle of a
  genuine republic."