Something that people really need to remember is the fact that we originally ended up settling on the safest region on the planet. So of course the other regions are going to be a lot more dangerous than where we started considering that we settled on a freaking deathworld that also happens to be an Old Ones, AKA the guys that could match the Necrons tech wise, bio weapons lab I have no idea why the fuck people are suprised at this kind of thing.
Odds are that the other regions are just as dangerous just in their own ways. Example, north is closer to the poles which are noted to be the most dangerou places on the planet potentially leading to us meeting creatures that may have migrated from the poles while the other option has us going across the freaking sea which are noted to have the most dangerous creatures on the planet which is the reason why falling into it is considered a death sentence. Choosing a region is pretty much picking our poison when it comes to expansion.