The government can’t keep these aliens in check. There’s no unifying leader, or even species. As far as the government’s concerned, they can do nothing. No one else knew about the aliens, politicians get no recognition for dealing with the problem. So the government just ignores it.
That’s where Sìofra Alma and Cara Smith come in. They are the only semblance of law on the planet. Too fair to be vigilantes, and too sensible to be bounty hunters. They are the investigators. Living among the criminals and bounty hunters of the galaxy, they care about the crimes committed on Earth.