"Q. Who told them to leave us alone?"
Sharing my viewpoint, belief, current level of understanding:
God. The Masters. A decree has gone forth. Any ET's interfering WITHIN the earth's atmosphere in anything but the Etheric realm are considered to be not of the light.
Humanity was designed as a free will creation that cannot see through the veil. That is part of our evolution here. It also has made us very easy 'pickins' for negative ET's and Power hungry ET's to deceive us (as we can see very clearly once we realize the PTB are non-human themselves).
The ET problem will be removed by the Ascended Hosts and humanity will be in the clear to make the leap in consciousness from the victim / slave consciousness always looking for a savior outside of ourselves (Jesus, ET's, Obama etc.) to realizing we're totally Self contained Beings that can depend on the source for our needs. We're not slaves, we're caterpillars about to be reborn as butterfly's and we'll co-create a Golden Age that surpasses anything this world has ever seen. Buckle up the seat belts, and surrender to the train conductor whose conducting in our hearts and we'll find we're in for the greatest adventure story in the history of reality