Nor fat, nor carbs are an essential nutritional component. The body can not synthesize certain amino acids, but it can convert protein to both fat and carbohydrates by means of gluconeogenesis. If anything, we should have cravings for sources of protein, not sugars. One could argue that sugars provide the burst of energy for the metabolic pathway that could be make it or break it in cases where that burst gives an advantage. This, and not the scarceness argument, which seems just thin to me, although mainstream opinion.
The very rough gist is that there is historical evidence of pre agrarian humans starving to death with stomachs full of lean meat. In a nomadic lifestyle where they chase down prey protein costs too much energy to digest and convert into usable energy.
Fat is an essential nutritional component. As an example, cholesterol is necessary to produce hormones such as testosterone, estrogen and cortisol. Thankfully, it's pretty much impossible to avoid if you eat meat.
Carbs are not essential. You can live on zero total grams of carbs.
Also gluconeogenesis only converts proteins to glucose, not fat, at least not directly.
