Conversation so far:
What was Gildas?
Gildas makes an allegorical condemnation of 5 British kings.
Why did he condemn them?
likening them to the beasts of the Book of Revelation.
What did he say about Gwynedd?
describing Maelgwn as the "dragon of the island" is appropriate.
Why was that an appropriate description?
The Isle of Anglesey was the base of power of the kings of Gwynedd.

Question: Why did he make these condemnations?
Self-contained rewrite: Why did Gildas condemn?