Fame
If you own a gun store, chances are you don't plan on being known for anything more than being a good gun store owner. That's actually a positive thing, because famous gun store owners are usually famous for horrible reasons.
For instance, there are gun store owners finding themselves in the spotlight for declaring being prejudiced against certain people. We're going to go out on a limb here and guess that you'll be trying to avoid that at all costs.
In the case of both gun store owners and whatever groups of people individual owners (inadvisably) choose to ban, it's wrong to dismiss an entire demographic based on individual actions. The vast majority of gun store owners are good people looking to earn a living in line with the law and fair business practices.
There are famous tough guys like Chuck Norris, Charlton Heston, and Clint Eastwood fighting for your right to sell your guns. But they didn't get famous for selling the things. Even so, it can be nice to let Dirty Harry do the dirty work.