Fish flakes are not flaked fish like layer pellets are not pellets made up of laying hens. With the difference that fish flakes have some fishmeal in them for the same reason that some brands of layer feed has fishmeal in it.
Fish flakes are what people feed their aquarium fish and what fish farmers feed their smallest fish. Bigger fish are fed the bigger forms like pellets.
They may have once been made primarily of just fish. They are not now.
Source
".. fish feed has economic significance. In aquaculture, the fish feed can represent over 50% of the operational cost. As feed costs remain high, finding quality feed at a reasonable price is becoming a challenge for many...
Since 2007, the National Oceanic and Atmospheric Administration (NOAA) have been working on ways to reduce their dependence on marine fish as a source of aquaculture feed...
Sources of protein are typically fishmeal ... legumes such as soybean....
Carbohydrate is an economical source of energy for fish. It helps to reduce feed costs. It can be useful as a binding agent when manufacturing feed, especially for feed that is designed to float. Carbohydrates make up 20-30% of many commercial feeds....
Another source
"...ingredients already in use include proteins from soybeans, corn, peas, and wheat, and oils from soybean, canola, and flaxseed. .., fish-based ingredient use for Atlantic salmon has declined from 90% in the 1990s to 25% in 2020."
Edit to delete what doesn't make sense and probably isn't helpful to anyone Even if I could get it to make some sense.