Fish keeping is more of a hobby than just another kind of pet

Many people see fish as being easy to keep for two reasons. First they are often cheaper. A 10 gallon aquarium may be $100 tops and you spend $5 on the fish. Versus for a dog you can spend $600 on the dog. If people spent $600 on fish for there 10 gallon aquarium, I'm sure they would worry a lot more about keeping them in the right habitat. However, when you spend $5 people see it as less significant and do not worry about the fish dying.

The second one, is a lot of common misconceptions. When people first get a fish tank, they are reluctant to get the proper size aquarium (hence all those betta bowls and similar you see). People keeping fish in these betta bowls has led to a lot of common misconceptions, along with the severely overstocked tanks at the pet store, and the unknowing workers. Few people know that goldfish can live up to 20 years, and if there goldfish dies in a year or two, they pass it off as old age.