We are discussing the reality that people can and do hang outside in the cold. It's not herculean if you are motivated to do it.

The matter of materials is not a nonsequiter - I don't know why those people you list did not use hammocks, but I can make a guess that materials derived from plants and animals degrade rapidly and need frequent replacement. This is after all why we use synthetics - cotton doesn't keep you warm and cotton thread rots in gear, which is why when engaged in any outdoors DIY project the recommendation in the directions is usually not to use cotton thread. Anything that bears weight will have additional strain. Suspension ropes and hammock fabric bear weight. If you are actively expending energy on a daily basis to hunt your food, are you going to spend it making hammocks or catching and butchering animals?

In cultures in South America many societies were not hunter-gatherers as in North America, so they were not out every day hunting and gathering to obtain food and living hand to mouth - their civilizations evolved to the point of specialization so there were farmers, hunters, etc and probably you could visit a Mayan city and barter a hammock from your local weaver. If I had to make a new hammock from animal skins or sit weaving it fresh from whatever plant materials I have available, I wouldn't do it either. I don't have the time. Since I have a paypal button, I can have nylon and down quilts, nylon hammocks, and sleeping pads delivered to my door with no extra effort to make it happen - I can spend most of my time making money to trade for materials that will probably last for years with proper care and keep me warm without issue.

So we are again discussing apples and oranges. We aren't hunter gatherers, and we aren't going to be needing to kill a buffalo to get our food and blankets.