I came across the following article that presents the hypothesis that the sudden apparition of cave art about 42000 years ago is linked to a geophysical event:
The temporary breakdown of Earth's magnetic field 42,000 years ago sparked major climate shifts that led to global environmental change and mass extinctions, a new international study co-led by UNSW Sydney and the South Australian Museum shows.
phys.org
In a nutshell: earth magnetic field inverted at that time and the magnetic protection it gives us against cosmic rays diminished, making caves suddenly valuable as shelters. Previous drawings may have been present, but painted on outside surfaces they would have disappeared with time.