The Outer Colonies are separate from Earth, with tenuous contact to the Core Worlds of humanity, and many were founded by small groups of people.  Historical Reenactors colonized Camelot for instance, though many question the accuracy of their reenacting.  In general though, people who went to the Outer Colonies did so because they wanted to leave everything and everyone behind them.  They went in search of a new life and they built it.  Their worlds reflect that.