system
A chat on subreddit /r/NoStupidQuestions
human
The geography of the central US doesn't really allow you to stay in one spot if you are part of a pre-industrial society. Soil quality isn't great, so to prevent the dust bowls that would form from later settlers, you have to move around a lot. Meanwhile, Central and South American soil is kept hydrated by being closer to the coast/the Amazon river, so you can more easily stay in one place, creating a need for technology to make having lots of people existing in a smaller space more efficient.
gpt
Additionally, the NA natives had different tech that suited their lifestyle. Instead of settlement-based agriculture, they understood how to farm/upkeep the natural landscapes. It's one of the reasons many settlers thought they had found "Eden." The forests of native NA were *flourishing* due to the native upkeep.