It's literally just because Tolkien thought Macbeth being killed by a man who was born via caesarean was a copout because of the "no man born of a woman" part of the prophecy.
It's the same reason why the Ents attack Isengard. He took the "you shan't fall until the forest marches upon you" and thought it was bullshit that it was just soldiers using branches from the wood as camouflage.
It's literally just because Tolkien thought Macbeth being killed by a man who was born via caesarean was a copout because of the "no man born of a woman" part of the prophecy.
It's the same reason why the Ents attack Isengard. He took the "you shan't fall until the forest marches upon you" and thought it was bullshit that it was just soldiers using branches from the wood as camouflage.