Well, that is a question which is quite easy to answer. Why?
Because the universe is unimaginable large; so large in fact that it’s infinite.
We live in the Milky Way; (which is one of billions of galaxies).
There are billions of stars and planets in the Milky Way alone.
Considering the countless number of stars and planets in other galaxies; it is not hard to imagine that a (tiny) fraction of those planets nearby stars also have the potential to support some form of life. Now, if we go a little bit further and say that even if 1% of those planets can support intelligent life; then it does not take much to realise that there is intelligent life out there in the cosmos.
Conclusion: we are not the only form of intelligent life in the Universe.
Criticism round the question; why have they not contacted us yet is actually quite simple to reject for several reasons;
First of all; Governments and agencies/organisations around the world are involved in cover-ups. Why? Well, there are three main reasons;
- There were many UFO sightings after World War 2; during which the Cold war started. Therefore, both East and West were suspicious of each other and wanted to gain military advantage by (using)/deciphering Alien technology.
- If governments or agencies/organisations would reveal there knowledge of extra-terrestrial intelligence, then religious people would be affected by that which can trigger riots; uprises and even wars.
- A potentially large portion of the general public would not feel easy with the notion of intelligent life in the Universe. This can also lead to civil unrest.