The free market doing what the free market does best. When politicians don't act it's impressive to see corporations take meaningful steps to try and solve the issue on their own. Dick's will probably lose a lot of money from this, but that makes it all the more impressive. At least they're trying to do something about it.
Second amendment, second amendment, second amendment. They still sell pistols, shotguns and high powered rifles so people are still going to kill others with guns bought from Dick's. This is a mental health issue, not a gun issue.
I agree that part of the problem is mental health. But guns are part of the problem too. Consider for a moment that every country around the world has people who have mental health problems. The USA is the only country in the developed western world that has mass shootings on this scale. They also happen to have the most relaxed gun laws. Certainly mental health is part of it, but if you can't see that guns play a role then you should look into it more.