The paintings always seem so beautiful, some even abstract. There seems to be a lot of artistic talent yet I've not seen many poor illustrations. Maybe certain caves and locations were important and reserved for the most talented artists to decorate and tell their story? I would have thought there'd be the odd practice wall found here and there.
I don't know if this is answerable in a historical fashion, since these paintings are from pre-literate societies. I could make a very strong speculation based on my knowledge of how artists in literate eras handled preparatory materials, but I think I would get in trouble with the mods. You might try /r/AskAnthropology, though.
One, not all cave painting are well drawn. When showing off public relations are likely to pick best examples. This depiction of a shaman at Lascaux is pretty crude by modern standards. There is certainly a style. Cross culture aesthetics are problematic.
Second, only certain artifacts and features survive several thousand years. So if I was learning how to draw cave painting using charcoal and bark it would probably be lost to history. If I drew in a place with exposure to elements it would disappear rather quickly depending on materials used.
Third, it is believe by most archaeologist that cave painting are often magic. Sympathetic magic relies on an object of similar design. It is possible that the individuals drawing pregnant animals wanted to imbue local animals with fertility. Caves are also believed to help create trance states. Remember that in the deepest parts of the cave there is less oxygen and pitch black. A combination of sensory deperivation and hypoxia could lead to trances maybe alongside botanical. So it's very likely caves were sacred places to the people that added art to them.
Other theroies suggest it's art for art sake or even educational. Ultimately we can't read the mind of the past. So there was probably practice with less stable (sand, exterior, bark, charcoal) medium in other locations which haven't survived.
You are asking historians about pre-history, but anyhow, consider that the evidence of prehistoric culture that we have simply represents what has survived, not what was necessarily the most common. The people who created cave paintings may well have spent most of their time painting and decorating wooden or other organic items and items not in caves - houses, boats, clothing, etc. All that is lost.
It's also plausible that decorated caves were already considered significant places before they were painted, and so only the most skilled artists were permitted to paint there.
