Well, they are "pet" stores . . . I don't really consider aquascaping a "pet" hobby. I mean, mostly a good aquascape is about the lay-out and plant selection FIRST, and fish selection SECOND. And as long as you don't pick lots of different dither fish, something harmful to the tank, discus/angels with colors that mess up the feel of the tank, or something way out there, you'll probably be ok and have lots of people say, "Ooh . . . what a beautiful tank!"
In the context of a great planted tank, a fish becomes just a fish . . . just an ornament in the display or the back-stage clean up crew. Sure there might be some stand out, but only the owner if anyone appreciates that fish's uniqueness/personality, and even then-- focus is still on the tank as a whole. I doubt Amano names all his otos and says "good boy! I love you so much!" as he watchest them eat algae.
In other words, aquascaping is more like Art, and a lot less like having a pet. Besides, how intimate a relationship can you have with a neon tetra?
Generally artists are a much narrower crowd, and there are a lot less places to cater to their needs. We all have to live with that fact here.
I personally can't expect petsmart to have a great selection of plants anymore than I expect a general store to have copic alchohol pens, Lining pens, painting knives or oil paints.
For good stuff, you will normally have to go out of your way.