Why Expand Gun Background Checks When Only 13 Were Prosecuted For Breaking the Law?

Congressman Harris asked Attorney General Eric Holder a series of questions about the background check system used when a person tries to buy a gun. For example, he asked why only 13 people nationwide were prosecuted for illegally trying to get a gun when over 76,000 were denied when trying to buy a gun in 2010. It begs the question, why expand the current system when it is broken? Shouldn't the focus be on making improvements?