Why do many wild people ignore use of plants?

I heard of bush people, amazon people, pygmies, massai, papuan people, they all hunt prey for food. I know that after the ice age, climate changed, it dried out, but the areas in which they live aren't so plant scarce. From the agricultural revolution, people have been primary farmers, the whole population was fed by plants. But along with the hunter lifestyle, people in the past have been gatherers of wild plants. As a primate species humans can digest fruits, leaves, stems barks, vegetables, grains like other apes can. Although grass is not edible, humans can digest special types of grass, barley, some types of grain and other. Example, bushmans (wild people of africa) live in savannah, the area of savannah hasn't got frequent trees and is abundant in grass, bushmans hunt the animals, I did not saw that they consume anything other, in savannah there are edible plants, baobab: the leaves, fruits and bark, gum acacia: the flowers that turn into seeds of acacia, look like pea pods, jackalberry: these trees can grow fruits, manketti: the flowers of the manketti tree, river bushwillow: the seeds of the tree, thorn acacia: the stems, barks and seeds. The bushmans hunt impalas, zebras primarily for food. The amazon tribesman also hunt, many plants in Amazon are poisonous, but there are edible, also the amazon people have cures for diseases and venoms, they could use that in case of eating poisonous plants. Savannahs don't have these plants I've mentioned on every corner, people would have to look for them, but in a case, there is no edible plants in savannahs, people would have to hunt, they can't eat grass, there are rare species of grass that can be eaten and are rarely recognized. Not all ignore the use of plants, but for god sakes we are omnivores, I did not see these wild people eat any plants, as species, the hunting, being a carnivore is not necessary. It is necessary to hunt animals, in areas such as deserts and poles, but it is not necessary to hunt animals which has vegetation that can be used for food. There are tribes which use plants, but why do some ignore if there are plants for use? The Hunza tribes are the longest living tribes and they eat only plants, the Inuits, Eskimos, have a lifespan of 50 years and they eat meat. Humans are hunting meat, because the closest relatives of humans, chimps, eat meat, they kill monkeys, birds, mammals, like humans, unlike humans and chimps, orangutans, gorillas don't consume meat. Do they hunt meat for apetite or they don't know which plants are edible?