One thing I never understood is how could the angels block access to Eden if they were stuck at the one entrance? Sometime, someone would have had the brains to create another one or simply go in through the brush. Even now, people are willing to break into or out of places by using off-road entrances, and Eden could no more be secured with guards at the official entrance than the United States border be secure by placing guards at San Diego. People will go around the blockades.
And yet, they would not go beyond that highly naive explanation--more symptoms of a Dark Ages mentality.