Why? Because there's an Eckert's on every corner.
A sniper would have to work very hard to find a place to shoot his victims that cannot be associated with an Eckerts' Pharmacy.
The guy probably chooses malls some of the time because there are always vehicles moving around somewhere in the mall lot which would draw the attention of potential witnesses, and the layout of most malls can make it very difficult for witnesses to determine the ultimate direction a getaway vehicle would take. The same goes for gas stations since they are usually on intersections and in really congested areas there are often parallel sideroads along the main drags; with all the potential escape routes and all the people and vehicles, witnesses are going to be quite confused.
Sounds like Waffle House in this neck of the woods.