What if, a few years down this 10 year timeline, something in the story happens that causes the Guardians to turn against the Traveler, and the light never came from the Traveler? Just a thought. Another possibility that Guardians will split into different groups (probably by class) and turn against eachother? Probably does not make sense now, but if they further develope a story to it, then we can understand this. Just another thought.