[polishdude20]

It could be that there's tonnes of people doing hand things with lots of different materials. Then, because of the composition of that red ochre material, only the drawings that were made with that stuff stick around for long enough for us to see them.

[divbzero]

Yes, and “long enough for us to see them” actually comprises two independent factors: (1) survivorship bias, in that red ochre on rock can last a long time, and (2) “discoverability” bias, in that red ochre on rock is relatively easy to spot.

[throwaway894345]

Additionally perhaps people (would-be discoverers) ignore art in remote places that is not a hand print or otherwise pictographic as probably a natural anomaly and not human-made?