The reason for that is the practices of fish farming has a reputation of being less than environmentally friendly in themselves, often and frequently less than clean. Although one of the cleanest ones (isolated GMO fast-growing salmon) faced the biggest pushback about issues they took pains to prevent (dessert located ponds are extra hard to escape from without someone delivers releasing live specimens) because people are stupid. All while complaining about water usage.

I suspect "premium" practices and standards might help here