Prehistoric people leaving things in caves is practically the only way we still know about them, but that doesn’t mean humans normally hung out in caves as a permanent lifestyle. We have evidence of people making wooden structures in Africa long before the first cave paintings—and compared to structures, caves would have been cold and dark, unlikely to be conveniently located, and contested for by cave-adapted animals.
It’s because the caves were so shitty that subsequent people left them untouched for tens of thousands of years.
There was a last major migration out of Africa starting around 70–50,000 years ago that coincides with both the disappearance of Neanderthals and Denisovans, and with the appearance of representational art. Earlier Neanderthals made artistic crafts like shell jewelry, but it wasn’t representational.