The problem is that it doesn't matter to many of these types whether they succeed and get away or not. Most mass shooters do not survive their attempts, nor do they intend to, they just want to go out blazing.In my local shop, that would be pure suicide. He wouldn't get off more than 1-2 shots. All of the employees, probably 12-15 at all times, are armed with loaded sidearms. This shop has probably 600-800 customers a day, mostly Interstate traffic, and has never had a problem. They also allow customers to carry loaded firearms as long as they remain holstered.
And this shop also allows customers to handle all the used, and quite a few new, long guns, on racks on the open floor. The pistols and higher priced long guns are behind the counter, but the have lots of employees to help.
Needless to say, with their large amount of business, this shop has tons of inventory and a coffee corner with couches and a big screen TV.
From an owner's perspective it doesn't much matter either. IF someone is successful in getting their hands on one of the shops firearms and so much as harms another person with it, the shop will be done for due to the almost certain lawsuits to follow for wrongful death, negligence etc.
All it takes is one... .