There are billions stars in Milky Way. There are billions galaxys like ours. Really you think that we are alone? That we are so special? There was 20 millions species on Earth. Only one is a thinking being but we are currently not not capable of long space travel. Moreover maybe they don't want to show up. Maybe space is big field of battle or used to be. If you want to exist you need to choose one of two options. You can try to cooperate with other civilizations but they can destruct you so if you want to be sure that you will exist is destruct them before them. This may lead to the hiding of weaker but still more advanced civilizations that could contact us. All of this makes the likelihood of an encounter low at the present stage of development. That doesn't mean they don't exist.
Join our clan. We like theories like this. You can be part of our hidden civilization. Now you can cooperate with us but you don't know if we not destruct you in the future.