Here's why:
* The play's themes: Macbeth deals with themes of power, ambition, and the supernatural, all of which were of great interest to James I. He was deeply fascinated by witchcraft and believed in the power of the supernatural.
* James's own lineage: The play also touches upon the lineage of the Scottish monarchy, a subject close to James's heart. The play even mentions the witches' prediction of Banquo's descendants becoming kings, which could be interpreted as a reference to James's lineage.
* Royal patronage: James I was a strong patron of the arts and a known admirer of Shakespeare. It's likely he would have seen multiple performances of Macbeth.
However, it's important to note that we cannot know for certain which play was his absolute favorite. There's no written record of his preferences.