Vex way’s of thought are based on pure logic. When something does not bother them they ignore it when something bother them they erase it when something is out of reach they adapt with logic until they can reach it. Per exemple based on the lore if we did not have the light nor the darkness and we didn’t try to fight them they would not fight us. Another thought, we still did not meet the vex warriors/soldier so does that mean we’re doing just as they planned? Will they be deployed only when we become a actual danger to them. As we know the destiny universe is a multiverses (we just get to see only one). is it possible that some universes do not have the light and the darkness. Per example when the vex passed through cropta’s portal they seem to have no information about the sword logic (which is the darkness logic). They would have information about it if it was on their universe. And my last thought, is it possible that some vex developed feeling or something. As we have seen with the harpy that did not attack us and even had recordings of failsafe last captain or when we found saint-14 statue built by the vex.