the main reason is quality of protein, without the need to highly process. whole ground cricket flour with no effort made to process or isolate and concentrate the proteins, has a better amino acid profile and more protein then pea or soy protein isolates. That and insect/animal proteins aren't chained the same way or locked in carbohydrate matrix, so they don't deplete the brush border enzymes in order to be made usable. The chemical structures are bio-available without complex enzyme intensive digestion.
don't get me wrong, i eat my fair share of beans and peas, and was vegan for 9 years, so i'm not against plant based diets, but there is a huge difference between protein quality, concentrations, and bio-availability between plant based proteins and insect and animal based proteins. It is a mistake to only look at the amino acid profile after the proteins are broken down. When you look at how the are bound, which enzymes are need to break those bonds, and how easily they are uptaken by the body for use, there is a very wide gap in difference. It takes a minimum of four times the energy and a ton of enzymes (which replenish at varying speeds) to get plant based proteins broken down to the same amino acids compared to animal proteins. during my early vegan days i believed the dogma that protein was protein and that we had too much anyway, once i started studying the bio-chemistry of it i had an eye opening revelation that those assumptions were very far from the reality. Fortunately the human organism can sustain itself on vast variety of food sources, our adaptability is no small part of our success story. In fact we might even be too successful !
Yes, but they are very efficient converters of those food sources. The amount you feed them versus the protein and nutrition profile you get is an order of magnitude more efficient then higher animal species, such as cows or chickens. Plus they can eat scraps that do not take away from the food chain, parts of plants that we wouldn't use for food regardless.