I was reflecting upon some of the recent arguments in the paleosphere around the ratios/percentages of macro nutrients that would compose a paleo-compliant diet. Let's start off with the premise that very little would go to waste - hell, we cracked open bone to get at marrow!
When considering macro nutrient ratios there are a few factors that need to be considered, not least the seasonal availability of plant food. But for me the elephant in the room is the utility of an animal carcass.
Let's not beat around the bush here, a carcass has way more utility than a plant when considered against the relative efforts to 'harvest' it. Let's put aside medicinal use of plants (I am not aware of many medicinal plants that could be considered a dietary staple), and look at what you can get from a carcass.
Think about something like an animal hide. You can use it for footwear or clothing - robust and warm clothing with thermal properties superior to many modern materials. You can use it for shelter - and importantly, the shelter is lightweight and easily transported. In the last 16000 years animal bones and skin have been used for lightweight and durable canoe and kayak. You can also make bags and pouches - useful for carrying water or perhaps your tools of survival...
As for the bones, as well as framing a canoe, you can use it as a handle for a weapon or tool. It could be used as an awl (for punching holes), a needle, a fish hook or a head for an arrow or harpoon.
And although we all hold an image of plant based twine and vines being useful for binding and hafting, sinew (tendon), is just as useful. And from sinew you can make rope or nets or fishing line. You could make thread, lacing or a bow string.
We could go on to look at feathers - for use as flights on arrows, or as a fill for either warmth or padding. Then there are things like the use of bones and skin decorated for the purposes of art and even musical instruments.
We can see the increasing significance of animal carcass in the anthropological record by the development of hunting tools and techniques (bows, spear throwers and harpoons).
I know that some of the tools above are were invented after the paleolithic, but my point is about the wider utility of animal carcass. Early peoples did not waste. If you forage for berries you come away with a limited meal and some vine. If you want a grass skirt or foliage for shelter (foliage which will have decay quickly and which will not be particularly transportable), then you need to make an extra effort to find and gather/collect.
In contrast, if you hunt a large animal and you have a nutritionally complete, energy dense meal and resource to clothe your family, to provide shelter and the materials to make a range or tools all in one 'package'. So where are you going to focus your energies?