Well first option is Ye Olde School Isolationism. The Venusian (Cytherian?) inhabitants at one point DID have contact and relations with other humans but stopped somewhere along the way. Wouldn't be the first time in history a "hermit kingdom" has emerged that kept to itself.
The second option is destruction of prior ties. You mention it's After the End, maybe the Venusian civilization is all that's left of the "old order" and the new ones either leave them be out of fear or no longer believing they exist or any other number of reasons.
The third option is the calamitous option. A great crisis or disaster befalls the Venusian civilization and the others simply think they won't make it even with aid. But they turn out into a civilization level case of Not Quite Dead when they finally do re-establish contact.
One thing to consider is that Venusian inhabitants may have adapted to some degree to the new environment and may no longer be able to survive elsewhere. If they tolerate and require a much higher oxygen partial pressure (left over from the decarbonization of Venus's atmosphere), say 90-80 bar O2 which is well above the pressure normal humans tolerate.
More prosaically, depending on the attitudes on both planets there may not be much interest on either side to communicate.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
Edited by DivineFlame100 on Jul 11th 2021 at 6:49:54 AM
Lost in Space
This is a thousand years in the future. A lot can happen in that time. Think about all the shifts in human civilization since 1000 CE: most of the nations from that time don't even exist now, never mind the cultures and languages. The possibilities are endless and can even be Shrouded in Myth: lost to history and remembered only as apocrypha.
While an "interplanetary war" like you see in Space Opera is unlikely, there can still have been incidents. Imagine a terrorist hiding a nuclear bomb in a starship and detonating it over a planet's atmosphere. A pandemic could have forced a quarantine on interplanetary transport. Something as simple as immunological drift can isolate populations as Venusians and Earthings become too different to interact safely.
You have a vast amount of time to work with.
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
Edited by DivineFlame100 on Jul 11th 2021 at 6:50:06 AM
Lost in Space
It doesn't have to be COVID-19; in fact that's not at all what I was going for. It's all but guaranteed that there will be more pandemics in human history. If you've decided that science and medical technology make that no longer a thing, then great, but it takes away a world-building element.
And yes, there would absolutely be people who freak out about the Dolls and try to blow them up, cut off contact with Venus, or whatever.
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
Edited by DivineFlame100 on Jul 11th 2021 at 6:50:17 AM
Lost in Space
It sounds perfect, in fact.
"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
![[up]](https://static.tvtropes.org/pmwiki/pub/smiles/arrow_up.png "[up]"){kind=icon}
Alright, I'll go with that and see how it plays. Thanks!
Edited by DivineFlame100 on Jul 11th 2021 at 6:49:43 AM