Why do audiences associate black-and-white photography and cinematography with a stronger sense of unidealized realism than that provided by color film stock?

cost was one of the major factor

Explanation: In the 1930s and 1940s cost was not the only factor determining which film stock a film project would employ, it was more. Hollywood Technicolor tended to make everything pretty, so that the most serious dramas often tended to be black and white: The Little Foxes (1941), Citizen Kane(1941), the entire genre of film noir, and so on.

Because it shows the naturalism of an art or object.

Explanation:

Cinematography can be described as  the art of motion-picture photography and filming either electronically which could be through an image sensor, or chemically by means of a light-sensitive material such as film stock

Photography is explained as the art, application and practice of creating durable images through the act of recording light or other electromagnetic radiation,  by means of an image sensor which is considered as the electronically means,  by means of a light-sensitive material such as photographic film which is known as chemically means.

Film stock is considered to be an analog medium that is used for recording motion pictures or animation.

In this case, the photography and the cinematography are considered as digital medium because they can be electronically operated, and produce objects in its natural form.

how is this a question?