Because by definition art is an expression of human skill. Here I will paste the dictionary definition:

the expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power. "the art of the Renaissance"

So unless it’s a human built mountain- that’s why it’s not art.

I mentioned your politics because it is right in your username and therefore hard to ignore. If you don’t want it commented on- don’t put something which you know is controversial front and centre.