Anywhere there's tough gun control laws, there's a booming black market for guns to be shipped in from other states. As long as there is a booming market, simply throwing people in prison isn't going to stop the problem. Is there massive amounts of money to be made? If yes, there will always be people willing to do it. Throwing all the gun runners in prison will just mean there's a vacuum that gets filled by new entrepreneurs.
When it comes to drugs, guns and anything else where there is money to be made, simply throwing people in prison does jack all to fix the problem.