Natives back then probably stayed fairly local (within 100 miles), and weren’t knowledgeable enough to realize they could move farther south and not have to deal with that. Any brave enough to explore farther south probably liked it, stayed and didn’t report back.
I believe you will find that native American tribes perhaps travelled more than many think. We find that around the world nations developed when
people share a common geography, customs and language.
An indigenous language map demonstrates how far a language spread in ancient times..and sharing a language meant travel could be effected
more easily for the breadth of their shared tongue..
During the revolutionary war, tribal members from the north went as far as the Carolinas and perhaps to Florida..
A language map shows how far certain languages travelled in anciient timess. Note especially the Algonquin (bright green) spread.
http://www.hartford-hwp.com/archives/41/048.html