Answer:
1. They are among the most popular plays to stage, so they are constantly being read by actors and directors who want to stage them.
2. Shakespeare is the most studied writer in English so students both at schools and Universities are reading him all the time.
3. Shakespeare's poetry is so great and his way of putting things so powerful that people mine it for great quotations.
4. The plays are enormously entertaining, so if you have the misfortune to be unable to see them performed on stage, or to see a film made from one of the plays, you can always read one and imagine a performance.