What ever happened to them? They there planet erupt in to war? Or so, Since the UFO Crashed long ago in 2065, Why is there a UFO who flys over, and explodes, 265 years later?
Are you refering the UFO in FO3? That's the only one I'm aware that has any bearing and consistency within the series so far, the crash sites in previous games were just special encounters, and had no official backstory as I understand it (not sure if this was the case for Van Buren)
If the UFO crashed in 2065, then it would only be 212 years later as FO3 takes place in 2277. I'm guessing they consider Earth a point of interest 2 centuries later.
There's no information in the series that points toward the prominence and/or abundance of otherwordly beings. Maybe Bethesda have something planned for the future, maybe they just want to convey that "we're not alone" and leave it at that, It's anyone's guess but theirs.