I just finished looking at that graph (in a Washington Times email I received this morning), and - at least in my mind - it tells us nothing about the possible reason(s) for the decline, which raises several questions. My initial reaction was, "This doesn't make any sense... Obama is a rabid anti-gun believer." And then the questions began...
1. What were the statistics based upon, and why did they drop so noticeably?
1a. The stats were taken from information available from the "Executive Office of U.S. Attorneys", which is a function of the DOJ.
2. Why would the DOJ make public any information of a type that would seem to imply that one of their bureaus is not doing it's job properly? As Alice said, "Curiouser and curiouser!" (she was so much surprised, that for the moment she quite forgot how to speak good English).
2a. Could it be because illegal gun purchases and gun transfers of other kinds have declined? It may be that those who are legally restricted from buying/possessing firearms have discovered new and creative ways to fool the ATF. I find it possible, but doubtful, that 'black marketeers' have reduced their sales of firearms. I say "doubtful" because those involved in the black market have enjoyed a lucrative return on investment for centuries. Money is THE great motivator for those who deal in the shadows, and they maintain a relatively 'exclusive clientele' in order to insulate themselves (and their illegal activities) from LE intervention. I find it more likely that, after a slight spike in 2012 during Operation F&F, the reduction came as the result of the chilling effect created by the public disclosure of the debacle the DOJ called 'Operation Fast & Furious'.
3. Could it be that by reducing the prosecutions, the Obama administration is hoping for a spike in gun violence, which would justify his push for more Draconian gun laws? In my mind, knowing a bit about the unusual and oblique thought processes of politicians, this is a distinct possibility.
I'm certain there are many more possibilities, but right now I can't come up with them. I submit this as food for thought, not as the ONLY possible reasoning behind the decline. I'm certain somebody in our group can provide other possibilities, and I hope you will do so. Pax...