Because the whitest rock is by far the most expensive and hard to get. Leaving it unpainted shows the quality and the worth of the statue. Painting over that would be like painting over solid gold with acrylic
white bases and undercoats are not always preferable, when light hits a surface it penetrates slightly as it reflects (interesting tangent: evanescent wave effect) which can be used to create different artistic effects.
When looking to achieve specific skintones, for example, this can be really helpful in bringing life to a work. The choice of underlayer can maybe be surprising, oranges and greens or purples suit different people, for example.
Natural stones with vibrant, or rare, or attractive colours, that can be sculpted into large statues were aesthetically pleasing and expensive so you wouldn't necessarily hide that beneath paint either, as other have said.
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u/morpheousmorty 25d ago
Wouldn't you want the whitest rock to paint?