I talk about some of history’s horrible famines in my economic development classes and the difficulty of getting enough food in Malthusian societies. Sometimes, some of my students ask why people starved rather than going out to hunt for food. The reason is that there are a lot more people than there are wild animals by mass. Vox did an interesting graphic comparing the mass of all living things on the planet. Here is the mass of humans:
In comparison, there is almost twice as much mass in the livestock on our farms. Note that the image of livestock mass below is scaled smaller than the image of human mass above, so you have to count the number of blocks to get a sense of the relative mass of humans versus their animals. The original image was scaled better.
Everyone cannot survive by hunting because there are a lot fewer wild mammals and birds than people and livestock. Even if they were all hunted to extinction, most humans would starve and that is why hunting has never been able to reduce the problems with famine.
During hunter-gatherer civilizations, population density averaged less than one person per square kilometer and there were a lot more wild animals compared with the mass of humans. Today every sovereign country in the world has a population density greater than that. Even countries in relatively inhospitable places like Western Sahara and Mongolia have twice the population density that hunter-gatherer societies had even in abundant ecosystems.
In theory, modern humans could easily survive by hunting and eating wild arthropods because there is plentiful biomass there to replace all livestock with vast amounts left over, but who wants to eat insects and spiders? There are also a lot of fish, but humans are already hunting and eating about as many fish as is humanly possible, to the point where it is already unsustainable, so it is hard to expand that food source.