It’s okay to include elements in a world without explanation. This can help create mystery and, in fact, can at times be a solution to problems that arise when worldbuilders are creating their world. As an example, maybe a worldbuilder wants to include a network of hibernating military satellites in orbit around a planet. This network was put in place by an advanced civilization. Only, as this world developed the worldbuilder decided to cut that advanced civilization from the setting completely. Now the satellite network has no reason to exist. And now that awesome narrative about ‘heroes’ accidently activating the network and unleashing powerful lasers that carve their way across the face of the planet to form new mountain ranges and oceanic trenches doesn’t make any sense. One solution to this conundrum is just to keep the network of deadly satellites anyway. If anyone asks where they came from, the official answer is no one really knows. They’ve always just ominously been there. Perhaps their background is a myth. Perhaps it’ll be explained later. But it’s vague.