Here's why:

* MacConkey agar is a selective and differential medium used to isolate and differentiate Gram-negative bacteria.

* Crystal violet is a dye used in Gram staining, a procedure to differentiate bacteria based on their cell wall structure.

Here are the key components of MacConkey agar:

* Bile salts: Inhibit the growth of most Gram-positive bacteria.

* Crystal violet: Inhibits the growth of most Gram-positive bacteria.

* Lactose: A fermentable sugar that differentiates lactose fermenters from non-fermenters.

* Neutral red: A pH indicator that turns red in the presence of acid produced by lactose fermentation.

In summary: While crystal violet is used in Gram staining, it's not a component of MacConkey agar. The selective and differential properties of MacConkey agar are achieved through the use of bile salts and crystal violet, lactose, and neutral red.