Why does the author view art as an unreliable source of social change?

because he does not think its important

I think it is because art is seen as the ‘sweet-spot’ to see things differently. Not 100% sure though.

Example:

"the idea of humanism is mostly adeptly reflected in renaissance art by a focus on the body itself, especially with sculpture, where many detailed portraits of the human body (such as the david) were created."