Why wouldn't they be able to migrate to lower altitudes or latitudes? It's totally possible to have similar genetics to modern humans and live primitively, we

Why wouldn't they be able to migrate to lower altitudes or latitudes? It's totally possible to have similar genetics to modern humans and live primitively, we have extant population in the Amazon basin, Indian jungles, Africa, maybe other places as well. It almost, but not quite, feels like an echo of the Ancient Civilization trope. Apropos, we find more indications of migration patterns through the ages, this one about Austronesian migration patterns and where their population originated from: https://www.artnews.com/art-news/news/7000-year-old-civilization-found-on-chinese-coast-illuminating-great-maritime-migration-mystery-1234691311/ https://www.artnews.com/art-news/news/7000-year-old-civiliza...