One of the main reasons that proves that texts don't have a use by date is the fact that an older text can involve events or ideas that are relevant to modern audiences' daily lives. Some of the ideas explored in Macbeth are ambition, guilt, greed, cruelty, hostilities between good and evil, the rule of leader, the purpose of human existence and supernatural happenings. These all tie in with peoples every day life.
For example, ambition was a major factor in Macbeth and plays an important role in practically everyone's daily life. In Macbeth it was ambition that drove Macbeth to commit the acts that he did and in modern times business is becoming more and more competitive in today's society so as a result ambition, and its destructive nature, becomes more of an issue.
Also, the idea of hostilities between good and evil, order and disorder and the rule of a leader, which are major components of Macbeth, are relevant to the military action in the Iraq War which has affected a lot of the world. These and other ideas interest people from all time periods as some, if not all, of these ideas will affect them.
Another main reason that shows a text doesn't have a use by date is the fact that they can always be appropriated. Appropriation is when something old is turned into something new. In this case it would be taking an old text and changing it to suit a modern