What always strikes me when people mention this is that everyone posts about living in the UK or possibly Canada or Scandinavia but no-one mentions Africa, South America or the South Pacific. These are locations where there are large areas of rainforest/woodland and hunting would have no restrictions if you wandered far enough into the trees. Alongside this the basic infrastructure or amenities in these areas are less than what is available in 'Western' countries so the potential distraction or temptation for rummaging in supermarket skips disappears. A huge number of people live in conditions that we would consider 'back in the day' and some in the deep jungles are stone age, people can and still do live like that in modern times so if you want to try it why not do it there instead of going through the same debate about lack of resources in these modern times.
This issue is, they live in communities. When you have a division of labor, among a tribe, lets say, you have a better chance at sustainment-hunters, fisherment, farmers, people working on upkeep, etc. When you have only one person doing that-its hard. Les Stroud did it for over a year, in Canada-he had a hard go of it, and said he wouldnt do it again. It was just him & his wife. When its only you, you are, literally, fending off starvation & dehydration, every single day. In a community, you arent, because you have more people doing the same thing, increasing your chances of making good. Even here in the US, the famous mountain men, and the voyageurs, didnt go it alone. They traded among each other, with natives, etc-as well as carrying a LOT of supplies with them, on mule trains. I think, and, this is my personal opinion, that people who want to return to a simpler life, are looking only at the idealistic view of it-the romanticized view. In reality, subsitence living is just that-scratching, day to day, for something to eat-and, again, being alone, or with only 1 or 2 other people, thats not living-thats merely surviving, when you are spending every waking minute hunting/fishing/gathering. Doing it for a weekend is fun-its a break from the realities of life. Doing it every day, is a job-one where, if you fail, you can potentially die.