If Wal-mart had adequate, appropriate oversight over its fish section, then customers wouldn't have the opportunity to dump multiple bettas into the same cups...or dump them into different ones.
Selling live animals requires a level of training and supervision greater than, say, selling shoddy clothing or housewares. Of course, the largest corporation in the world can't afford to properly care for the animals that it sells. So the animals suffer.
I quit shopping at Wal-Mart altogether several years ago. I don't like their record in terms of treating employees, including returning veterans, poorly (and in many cases, illegally). I don't like the experience of shopping in their stores. And I don't like how they treat the animals that they sell. If they cared to do better, they easily could. But they don't.
Live fish are a loss leader for Wal-Mart. The only way to make an impact is to stop shopping there altogether. And let company leadership know why.
Matt