We don’t really get much about the Edo other than what’s immediately relevant to the plot (and the skimpy outfits), so there are many possibilities. The Klingons, Romulans, Cardassians, or even Ferengi may have been the first to make contact, and the Edo God doesn’t seem to mind outsiders so long as they don’t try to settle permanently. The Edo also could have been space-faring in the past and decided to scale back. Or maybe they are warp-capable and very few care enough to leave the planet.