Fish keeping is more of a hobby than just another kind of pet
Fish keeping is probably closer to a hobby than having another pet, especially in the case of keeping large aquariums with many fish rather than just a single one.
Many people mistaken fish as "easy to keep". It is harder than most people think. They often die within weeks, days, or even hours and minutes after they've been put into a new tank. People overlooked the importance of doing research before having fish. With other pets such as a dog or a cat, no way they will die that fast no matter how horrible the pet keeper is. Fish is just so much more fragile, and they will die when the keeper make a mistake.
Nobody should get into fish keeping hobby without extensive research first. Or the poor fish will get it...