A point of brutalism is "form follows function and "showcase the bare building materials" (1) - in other words, that's how the material looks, naturally. Bare, unpainted concrete is in fact more natural and honest than painted concrete. And brutalism deliberately leans into that naturalism (of modern materials).
The impression of Unnatural comes from the fact, that brutalist forms don't exist in Nature. Concrete is everything but not a natural material. Showing it isnt natural.
I am still buffed they are people defending brutalism. It is one of the biggest mistake in Architecture and one day these buildings will vanish.
A point of brutalism is "form follows function and "showcase the bare building materials" (1) - in other words, that's how the material looks, naturally. Bare, unpainted concrete is in fact more natural and honest than painted concrete. And brutalism deliberately leans into that naturalism (of modern materials).
1) https://en.wikipedia.org/wiki/Brutalist_architecture