So here are a couple of thoughts that have been rattling around in my head re: 3i/Atlas.
Assuming it is not of natural origin:
1) There has been lots of speculation about why an alien race would bother to send a vessel here given the time involved. What if it was a mistake? What if someone just forgot to set the parking brake?
2) Maybe it is a "catch me if you can" scenario? It is sent out and if a civilization is advanced enough to physically intercept it then they are of interest to whoever sent it. If they can't then they aren't important enough to matter.