A huge part of it-and this doesn't excuse it, just explain it--is the prevalence of myth in the hobby. "Fish only grow to the size of their surroundings." Raise your hand if you heard this--won't make anyone admit to buying it, but we've all heard it.
And of course, people recall their Aunt Esther kept a goldfish alive for 15 years in a bowl.
Most people--including many who have been in the hobby for years, have less understanding of fish biology than they do of astrophysics. They do not understand the biology behind maintaining a tank, or providing for the fish. It's not like mammalian pets--we understand cats and dogs better, because we share some of their needs. We can see the waste from them, smell it, and know it's icky. With clear liquid waste, in a box of clear (mostly) water, the wastes are out of sight, and easy to ignore.
So, ignorance is the reason. That it is willfully maintained is beyond my understanding, but there it is. People are happy being uninformed. Heck, I've had people argue with me about some of these things. Just mention using iodized salt in some places, and you will get looks of horror. Mention that you would love an oscar, but don't have the room, and someone WILL tell you it will be fine in a 10. Or--and this has happened--ask if you can put a betta in a community tank. Just see if you don't hear that either the betta will drown in the deep tank, or that it will kill every fish you try to put in there.
And of course, people recall their Aunt Esther kept a goldfish alive for 15 years in a bowl.
Most people--including many who have been in the hobby for years, have less understanding of fish biology than they do of astrophysics. They do not understand the biology behind maintaining a tank, or providing for the fish. It's not like mammalian pets--we understand cats and dogs better, because we share some of their needs. We can see the waste from them, smell it, and know it's icky. With clear liquid waste, in a box of clear (mostly) water, the wastes are out of sight, and easy to ignore.
So, ignorance is the reason. That it is willfully maintained is beyond my understanding, but there it is. People are happy being uninformed. Heck, I've had people argue with me about some of these things. Just mention using iodized salt in some places, and you will get looks of horror. Mention that you would love an oscar, but don't have the room, and someone WILL tell you it will be fine in a 10. Or--and this has happened--ask if you can put a betta in a community tank. Just see if you don't hear that either the betta will drown in the deep tank, or that it will kill every fish you try to put in there.