Because in Fallout 4 the protagonist, the male Sole Survivor Nate narrates his own beginning & end is because he's a future antagonist. The last DLC was the protagonist becoming a Raider boss & I don't see an achievement for 'Open Season'. My fan theory is that the protagonist could be the antagonist of the next Fallout game, the protagonist of Fallout 4 doesn't have a morality system, there is also the Rust Devils the protagonist could add to Nuka-World.