Here's why:
* The Ghost is a Supernatural Entity: The Ghost is not a real person, but a spirit from beyond the grave. It can't be "spoken" by anyone other than the actor portraying it.
* Stagecraft and Illusion: The Ghost is a theatrical creation. Shakespeare likely intended for the Ghost to be portrayed by a visible actor, creating an illusion for the audience.
* The Ghost's Role: The Ghost is essential to the play's plot and character development. The actor portraying the Ghost needs to be able to convey the Ghost's emotions, motivations, and messages clearly to the audience.
So, while the Ghost is a fictional entity, the actor portraying it brings it to life through voice, movement, and performance.