I am not sure that fish(like very small anchovy) is in grade to effectively feed humans.

What does this mean? Anchovies are normal food sold at the supermarket.

https://www.tesco.com/groceries/en-GB/products/306930957

https://www.tesco.com/groceries/en-GB/products/310103367

that's likely larger and more mature presorted units. Salmon can eat smaller ones. You can tell from the price that those cost more than actual salmon.

I am not expert, I am just speculating that if you dig into details, picture can be very different.

This outright silly, salmon tastes better and thats why people eat it. There isn't some great mystery about small fish being less edible.

I regularly go to the fish market, small seafood like anchovi and shrimp can be bought 4 times cheaper than salmon.