They don't listen simply because they don't want to. I mean, say you are one of these fops and got a brand-new 5 gallon tank and (hopefully) cycled the tank. THen you go to Wal-Mart or the LFS, and this strange man comes up to you. He's very strange because... he.... cares about the fish... hmm. He then tells you the goldfish you SO desire in your heart will not fit in your tank comfortably. Since you have seen these stereotypical pictures of goldfish in a bowl/small tank, you disagree with him.
After all, he said "They won't fit" and you have seen 100s of pics with goldfish in bowls! A picture means 1 million words and he said 3 simple words, so you MUST be right!
^^ THAT'S their mentality.