Specialty hardware (woodworking, etc.) is something that WalMart can't handle. Fish/pets is another good example. Managing a pet store takes skill, good knowledge of your stock (it doesn't just sit there like floor mats and cheap shirts), and LOTS of hard, devoted work.
No way some part-timer in the WalMart who looks in on the fish after dusting the Rubbermaid stuff and sweeping the floor is going to be able to keep those little finny fellows swimming upright (instead of doing the back float on the surface), let alone looking chipper and frisky in a nice clean tank that says, "Buy Me!"
We did tropicals for years and then branched out into salt water. Once we were living in a place that allowed cats, we switched to breeding and showing Siamese cats. Now we're doing obedience and agility with a Chocolate Lab. . . . WalMart can do none of the above.
Working your way right up that old foodchain, eh?