In Egypt, actors were not allowed to testify in court because they were seen as professional liars
Today, professional actors are renowned for their talent and celebrity. They're worshipped by fans and stalked by paparazzi. However, back in Egypt, professional actors were equivalent to professional liars. In fact, historical views of actors often saw their work as disreputable.
Audiences had a hard time distinguishing between the illusion of acting and real life. As such, actors in Egypt were not allowed to testify in court. As "professional liars," they could easily dupe the judge and wreak havoc on the system.