I worked for a medium sized chain pet superstore years ago. It's privately owned and the owner of the company uses his friend's fish wholesale company to supply fish. just FW, they experimented w/ salt in my store and we kept them healthy but they just weren't cost effective. Anyway the problem with the fish was the entire operation. The fish that came in were usually highly stressed, and diseased. Medication was standard procedure for all new arrivals. There were numerous complaints by employees about the poor quality livestock coming in but the complaints fell on deaf ears. We would pull out nearly 10% of the entire fish population daily due to deaths. There was little the employees could do. All of the tanks were on one linked system with a central filtration system, similar to most large operations. So if one tank was diseased, they all were.
The bottom line when dealing with livestock in large chainstores in general is just that, the bottom line. When one considers the costs of feed, bedding, water, electricity and floor space devoted to the livestock the stores are operating at a loss. They make no profit selling a platy or mollie at $1.29. or a neon at $1.49. the reason they have animals is to get you to buy the dry goods: tanks, cages, food, treats, chemicals, lighting, etc., and keep you coming back for these items. Why do you see so many promotions for a free hamster/ gerbil with the purchase of a cage? The store that Tom_Nev went to is just looking at costs. Why take medicine off the shelf that will bring in $5.00 profit to save a fish that will only bring $.50 profit? It's just not good economics. Livestock or medication or food, it's all just a product to sell. Movie theatres do the same thing. The theatre doesn't make that much money off each ticket sale. The money comes from concessions. The tickets just get you in the door so you can buy the $4.00 soda and $3.00 popcorn.
The laws usually only care about the warm and fuzzy animals.
It's just business.