This is a way for shitty writers to justify infodumping in their story. If your main character doesn't know shit about the world he just got put into, you can justify every other character dumping a huge load of setting and world building down his ear canal. Instead of, like, trying to mix that info naturally into the story, which also avoids the "as you know, John..." trope (where character A explains something to character B that they already should know), but requires effort and skill on the part of the author.