It's simple. Chunk style tuna in water leaves a lot for waste fish. When I was a kid each can contained a large cutlet, complete with a piece of spine. So make smaller cans to take the sections from the tails. Still a lot of left overs being turned into chicken meal, so the next step is to scrape small chunks of fish from the skin and bones and can that. That's the small snack size tuna in spring water sold at a premium price. There are still small fragments of flesh. Pressure cook the remains to bring all the little pieces off, skim them, fill a fan with pressure cooked scraps plus oil to give it some body, use Sneed oil because this is pleb food.
Increasing international demand for a fixed number of fish (rise of China and Korea) means the Western premium cans need to downgrade their quality. So they swap to using pressure cooked scraps, and add flavours to hide the fact that the scraps taste like shit compared to whole tuna.
You are here.
The next step is to move to farmed fish only, the 2030 ban on internal combustion engines will end commercial fishing by 2050 at the latest. Then the fish farms will gradually shut down as well because krill for fisH food will not be caught. Then you will eat the bugs.