Parents teach little ones from birth about chickens, pigs and cows. And so it is, even though there is no nutritional need for meat. Hamburgers and pork are quietly disguised. We don't call them cow or pig. I think the meat industry somehow missed by not renaming chicken.
Fish is called seafood.
The word food is built right into the name, like they have no other purpose than to be eaten. I would visit aquariums, snorkel in Florida, and had a fish tank in my home, but these fish were somehow different from the fish I ate. The TV commercials from the fast food places are everywhere. Especially on the Saturday morning cartoons. And the highway billboards are everywhere too.