You’re going to have to be more specific, because it’s highly inaccurate to suggest that basically any indigenous group in the Americas lived a “caveman” lifestyle prior to the arrival of Europeans.

Lion-man figurine is dated to, from the article you linked, 35,000 to 40,000 years ago. This is thousands of years before the first signs of agriculture developed in the Middle East. In contrast, by 1492 agriculture had been established in the Americas for thousands of years. Much of the eastern and southwestern United States was populated by settled farmers residing in urban centers, not hunter-gatherers. And groups that might fall under “semi-agriculturalists” were hardly small, nomadic tribesmen. Take the Calusa of southern Florida, who may have practiced limited agriculture but not to the extent of their neighbors - using a triad of fishing, hunting, and gathering, the Calusa established large, permanent cities with a complex state structure and hereditary elite, and were praised by the Spanish for this. This is night and day from what a “caveman” would have lived like. It’s comparing apples to oranges.

No human civilization is an island. There are very few civilizations that have been entirely isolated from any other, and those “exceptions” you cite in the Americas had contact with neighboring, less urbanized societies. Pre-Columbian trade networks spanned continents; we’ve found Mesoamerican artifacts in Oklahoma and goods from the Pacific coast in North Dakota. “Cavemen” lived in a world where no one had developed agriculture, where technology as a whole was extremely limited. This was not the world of the Americas in 1492. The situations are not comparable.

This is not to disagree with your hypothesis. That far back is not my specialty, and I do hope someone with knowledge there can chime in. I think it’s likely many “cavemen” societies were much more complex than we give them credit for. But I absolutely do not agree that it is comparable to the Americas pre-contact. These are drastically different situations.

[I had to rework this post a couple times because I was getting bogged down in details, and unfortunately it ended up pretty "meta" in part because the simple answer "because that description in Wikipedia is inaccurate" has a lot of backstory. But if there is anything that needs expanding on I am happy to do so]

Leaving aside the important point regarding the contact era Native Americans that arkh4ngelsk made, I think you have hit upon an important point here: if the Cro-Magnon/Upper Paleolithic foragers ("cave men" is, as noted, an obscuring term, both because while caves preserve materials well they aren't actually habitation sites, and because it is often used to conflate Neanderthals with homo sapiens hunter gatherers) were so materially impoverished, so beset by the environment that they had little time for anything besides the simple matter of seeing to necessities, how did they create beautiful figurines like the Lion Man? How did they develop artistic skills to such an extent that the paintings in Lascaux were possible?^1 The answer is, you know, their lives probably were not like that. Their lives were probably not all that bad, full of hardship for sure but not to the exclusion of all else.

I will make this a quick digression because I actually think the question of human welfare and cultural complexity is somewhat different. Generally, the idea that people who live seemingly more primitive lives than "ours" actually live better in some ways is very old--it is there in Hesiod, it is there in Tacitus, and of course it is there in the idea of the "noble savage"^2. Academically an important point is Marshall Sahlins' essay "The Original Affluent Society", in which he took anthropological research of hunter gatherers in the Kalahari to argue that far from being the debased peoples on the planet, they were materially more secure than most people in the world, let alone early agriculturalists, and had abundant leisure time. Over the last sixty odd years this argument has been subject to endless debate and challenges and supports from theoretical and empirical grounds and I will not touch on that.^3 Conceptually the important point that has stood the test of time is that we cannot take the "stages" of material development as "stages" in increasing human welfare, and in particular the transition to agriculture--far from being the key unlocking human flourishing--was actually a pretty rough deal. It is an essential insight, for example it is an important part of the debate about whether agriculture spread via farmers populations spreading or through hunter gatherers adopting the new technology. The archaeologist Peter Bellwood for example argued for population spread because it is very unlikely that hunter gatherers would want to become farmers--and genetic evidence has now more or less confirmed that agriculture spread through population expansion.

This is all related but distinct from the idea of cultural complexity. There is something of a pop culture idea that hard times and hard places breed hard men, practically minded who cannot be bothered with the niceties of society as they are too focused on survival and their situation demands stark simplicity. But really nothing could be further from the truth. Anthropological research into modern hunter gatherers has shown astoundingly complex cultures--to give one easily accessible example, Wikipedia has a list of mandates and taboos for Inuit women during childbirth, but also if you read Things Fall Apart in high school you will be well familiar with the idea that the seemingly simple and primitive cultures subject to Western domination were in fact extremely complex.

Although we cannot anthropological detail the paleolithic peoples of Europe, we can still get some hints at the complexity of their society. The art is an obvious example, from cave paintings to small figurines to beads to the pleasing aesthetic quality of spear points. But we occasionally get something a bit more detailed--there is more or less an entire archaeological subdiscipline of reconstructing camp site organization from the deposition of the remains of flint knapping, yielding examples^4 such as where the evidence of superior craftsmanship occurring closer to the fire, implying that more skilled craftsmen had a position of privilege--this is practical, perhaps, but also certainly an example of complex social regulation. There are also burial sites that yield some sort of hint of cultural complexity, such as the Sungir burial near Moscow that included two adolescents with a rich array of grave goods. It is much too far to use this as an example of emergent class stratification, but certainly something is going on here beyond the simple struggle for survival.

To zoom back out somewhat, there are two assumptions lying behind that sentence from Wikipedia. The first is that Paleolithic life was consumed by the never ending and always precarious needs of subsistence, the second is that this constant struggle produced societies that were austere and simple. The first assumption is highly questionable, the second is flatly incorrect.

The literature on this is vast, but if you are curious about Paleolithic Europe, I cannot recommend Brian Fagan's Cro-Magnon as a wonderful and accessible introduction enough.

^1 Worth pointing out that the Lion Man figurine is about as far distant from Lascaux cave paintings as Lascaux Cave painting are from us.

^2 "Noble savage" is a term that is often deployed in these conversations, usually inappropriately, and for some reason I cannot possibly fathom with more of a cautionary tone than the myth of human progress as measured by increasing material abundance.

^3 This also dovetails with a related debate over the question of "subsistence affluence" in developmental economics.

^4 I am blanking on the site here that gets used in every 101 class but I will insert it when I remember.

When Hobbes described life in the state of nature as solitary, nasty, brutish, and short, he was most certainly mistaken, though influential nevertheless. Darwin's Malthusian popularizers like Herbert Spencer infused biology with the political perspective of Hobbes. It's part of the words used in the discourse, people aren't even aware of it.