I work for an intelligence agency of a country I will not be naming (not flag). Aliens are real but they don't engage with us because they can't beat us. Why? Keep reading.
Throughout our history, humans have developed extremely effective manipulation techniques that allowed us to manipulate animals into servitude. We lure them with gifts and in turn they become pets, cattle and beasts of burden. Aliens are succeptible to this too. Since aliens come from planets with abundant resources, they have not developed this very specific manipulative, behavioral strategy and are not evolutionarily adapted to recognize it. Research done in the headquarters of my agency has shown that aliens are succeptible to treats and pats on the head.