Too unpredictable. The Light allows us to bend reality, which means each simulation of a single Light requires a certain degree of wiggle room. You can’t never be [i]exact[/i]. That uncertainty factor compounds and multiples as you add Guardians, especially a few thousand. Not to mention the Traveler itself. Or they might not want to. They may need the Traveler for something. They are master schemers. The Vex also have a lore line about how they can manipulate us despite the flaws in their sims about us. See they can sim everything around us that is normal. So if you maneuver those normal pawns right, Guardians would be in a position where we are forced to do certain predictable things to solve the situation. It’s a sound plan, makes perfect sense lore wise. Asher has said a similar thing.