To get a lot lighter: "It was all a dream," or, "It's all in their head," are easy fan theories to attach to works of fiction because that's what actually happ

To get a lot lighter: "It was all a dream," or, "It's all in their head," are easy fan theories to attach to works of fiction because that's what actually happened. The creator of the fiction imagined it in their brain. You can trivially apply it to any fiction without any creativity. More complicated fan theories rely on the content itself, and thus are going to change from work to work. So people hear "It's all in their head," more.