I think part of the problem is, everyone knows dogs, cats, birds, etc. I mean, a Great Dane is big, eats a lot, etc. A Husky sheds a lot. Chihuahuas are small. Cats have long hair or short hair. They use a litter box. I mean, most people have at least an idea what's going to go on with a dog or cat.
Fish though...I doubt many "non fish keepers" have ever even seen a mature Pacu, Gar or even a fully grown Oscar. Most every single fish they have ever seen has been in Petsmart or Wal Mart. They do look cute! And run what? $3 to $5 average? Everything the non fish keeper knows about fish is they are small, pretty, cheap...and living inside a 24" X 20" X 12" box, they can't be hard to take care of, right?
A nice looking 20 gallon tank with filter and light isn't priced bad either, $50? (they don't tell you that you need a $40 heater). So I can see people getting excited that for $100 or less, they can walk out of the store with a shiny new tank, some pretty colored plants, flake food, dechlorinator, ammonia reducer, some multi-colored gravel...and 6 bags of 1" long fish that together are nearly every color of the rainbow!
It would be cool if the tank suppliers had a pamphlet on the box that at least had the basics. Briefly explain water changes, capacity, fish size, etc.
Anyway, that's my thoughts. Doubtful those 6 bags of fish made it long...