Actually, fish require careful and constant upkeep and the vast majority of fish owners house them incredibly poorly. Why? Because like you, they think fish are simple and easy to keep. Goldfish don't belong in bowls, for example; a goldfish will grow to its environment and requires a pond eventually, even though it's small now. If you keep it in a bowl, its organs will keep growing but its body will remain small, and it will die within a year or two usually, and it will suffer greatly.

Each species needs to be carefully researched and has its own needs. Most people don't bother doing this research. Very frustrating for people like me who love fish.