Time: Shakespeare wrote his plays in the late 16th and early 17th centuries, and the language and culture of that time are very different from our own. Many of the references and allusions in his plays are now obscure, and some of the puns and jokes are no longer funny.
Changes in language and culture: The English language has changed significantly since Shakespeare's time. Many of the words he used are no longer in use, and the meanings of others have changed. This can make it difficult for modern readers to understand what Shakespeare is saying.
The limitations of the printing and publishing processes: In Shakespeare's time, plays were printed in quarto editions, which were small, unbound booklets. These editions were often poorly printed and contained errors. In addition, many of Shakespeare's plays were not published until after his death, and some of them may have been lost or destroyed in the interim.
As a result of these factors, it is estimated that about 20% of Shakespeare's writing has been lost to modern readers. This includes at least one play, "Cardenio," which is now considered to be lost forever.
Despite these losses, Shakespeare's work remains one of the most important and influential bodies of literature in the world. His plays are still performed and studied all over the world, and they continue to be a source of inspiration and enjoyment for people of all ages.