Some people believe that Shakespeare isn't the true author of his works because

There was no record seen by Wilmot, to show that Shakespeare read a book, let alone write a letter.

Explanation:

James Wilmot, a reverend and literary scholar came up with an idea in 1781 that Shakespeare was not Shakespeare. He went to the house that William Shakespeare lived during his lifetime, and went through all the libraries in his Stratford residence and searched for correspondence.

There was no record seen by Wilmot, to show that Shakespeare read a book, let alone write a letter. He did not find Shakespeare signatures on the bottom of the old letters that were seen. He also stated that there was no property, belonging to Shakespeare, that was written on the on the endpapers of a Bible.

James Wilmot concluded that the plays of Shakespeare could not have been written by someone who did not leave an literary paper trail behind him.