Why? Well, because the president’s defenders like to mock those among his critics who argue that he wants to “take their guns away.” As of today, they will no longer be able to do so.
At present, there are around 350 million guns in circulation in the United States — more than one for every person living here — and the American people enjoy constitutional protection of their right to keep and bear them. If the American government did what Australia did in 1998, they would bring in about 100 million guns but leave between 200 to 250 million on the streets (about as many as there were in total in 1994). This, obviously would be rather pointless. More important, perhaps, such a move would lead to massive unrest, widespread civil disobedience, and possibly even a war.