I went to the local WalMarts yesterday and looked around.
WalMart guns are in the sporting goods section with fishing, boating, kayaking, etc. outdoor sports. Sporting guns has always been WalMart's stronger point. I think WalMart stocking ARs was a step into a market WalMart simply could not serve well at this point in time.
We do have local gun dealers who do specialize in defensive guns, civilian marksmanship practice, military surplus, active duty police equipment, etc., who I feel are a better fit with the AR market. Their staff often assemble ARs from lowers, FCGs, uppers and stocks, or own ARs and hunt or compete with them.
We do have an increasing number of military vets getting into civilian hunting, plinking, self-defense, etc. and who see no reason to switch from AR to a platform where they will need to retrain safety and handling. After the Civil War, the civilian sports market accepted the lever action repeater. After the Spanish American War and WWI, the civilian market accepted the bolt action rifle. There is a possibility that WalMart simply tried to enter the AR market a half-a-generation too soon.
I have noticed around here that what WalMart stocks is seasonal, too. Muzzleloaders and supplies are present just before and during ML deer season, and after close of the ML hunting season, any remainders are sold off to clear space for the start of boating/fishing season. To find a WalMart that stocks reloading supplies, I had to drive forty miles though; most don't carry reloading supplies at all.