I think an issue comes from conventional care needs of something terrestrial vs aquatic. For something like a hamster, giving it plenty of food and treats, deep cleaning its cage, change the bedding so it is spotless even using something like a antibacterial wipe. That will result with a thriving pet. People think fish will be the same, give them loads of food, then once a week/month wash the 'dirty' gravel and filter under the sink and then change all the water for nice 'clean' water out of the tap. We all know that would/does end in disaster.

Also I think stuff like the classic 'goldfish bowl' gives the idea they don't need much in terms of care and flushing fish down the toilet when it dies (as appose to burying it like a cat or something) gives a sense they have less worth, both don't help.