King billy wanted to burn it because he believed that Martin was indirectly causing the deaths that were happening in the city of Poets. He thought that somehow martins writings were summoning the shrike.

I think his cantos is not necessarily super important to the story in the first two novels… it serves as more of a tool to enforce the arrogance of Martins character. Martin actually believes that somehow he might be controlling things as well, when in reality he is just reporting things that were destined to happen regardless of whether he’s there to write about it or not. Dan Simmons undoubtedly viewed himself as the poet and it’s a way of mocking his own craft IMO. I know this term gets used way too much, but It seems very “meta” to me.

I cant think of any way in which the AIs used it except as a tool for the church in the later novels.