Why do some people think Shakespeare may have not written Macbeth?

The real Shakespeare, the one who wrote the plays, was brilliant philosopher Francis Bacon. Or it was romantic and tragic Edward de Vere, Earl of Oxford. Or it was secretly Queen Elizabeth. Or Shakespeare's rival playwright, Christopher Marlowe. (Christopher Marlowe may also have been a spy, and some conspiracy theorists will tell you that he faked his death. The man got around.) Or it was a whole group of people! Maybe it was all of them? Even the Supreme Court's gotten in on the argument. In 1987, Justices John Paul Stevens, William Brennan, and Harry Blackmun held a mock trial on the authorship question. Brennan found in favor of the Stratford man, but Stevens and Blackmun weren't so sure.