Question

Why would an author use an unreliable narrator

Answer 1

like what would be a reason

Answer 2

it depends on the genre of the work. if it's fiction, they may use an unreliable narrator so the reader doesn't have prior knowledge to a twist that will come later. i'm not sure what else, but that's the first thing i thought of

Answer 3

this website may also help
https://www.thebalancecareers.com/the-unreliable-narrator-in-fiction-1277141