Why do aliens always look like us

Contemplating the possibility of life elsewhere in the universe. We think of aliens and immediately cut them down or up (or some other inconceivable dimension) to our size. They can be bigger or smaller, their heads huge, their eyes bulbous; they are usually humanoid, occasionally reptilian, but they are always recognisable as variations on the theme of life on planet earth. This is as true when we set out to imagine alien behaviour as it is when we imagine their shape. They always have humanoid sentiments which can be reached by us,

This kind of thinking is anthromorphism writ large. We employ this kind of thinking to make sense of things.  In Christian theology, God, (Jesus Christ) is a man with a beard.