They may be living with us now studying us and to see if they can adapt to earth and survive here. They may be trying to guide us to be a more peaceful race so that we can work on actual advances in medicine and technology that helps and does not find new and exciting ways of killing each other.
So many theories but will we ever know the truth, I doubt, if there was any clear answer they're doing a lousy job of letting us know what it is Unless the governments know and are keeping it under wraps.