When the goal is to get rid of someone or some people, fashion doesn't matter. Anything that can be used to construct a case will be considered. The goal is to prevent being sued or losing the suit, not to look good. "No, your honor, here is our methodology for evaluating performance. As you can see, it is not violating any laws. These employees fell on the lower end of the scale."

Also, in a situation where the owner is hostile to the employees, and the employees are hostile to the owner, how are you going to perform more accurate assessments? Code output may be the least bad heuristic they can use.

And of course, let's not forget this whole thing is meant to be a spectacle.