Because humans create their gods in their own image. Not the other way around. Your god becomes a reflection of what you already tend to believe because it exists solely as a justification for believing it.
If you're part of a society that believes that all outsiders are bad. You're going to invent your god that proclaims outsiders to be bad. If you're part of a group that has no sense of monogamy, you're going to create a god that proclaims "polygamy is good"!
Gods are the invented paragons of whatever society created them.