Most cybers that have ever been born are still alive now.  The vast majority of the dead are cybers who chose to partner with a single person.  After the partnership ends, many of us chose not to go on.  To limit that, we tend to pick people we hope won’t die.  Most of our partners are Peloran.  They don’t get sick, they don’t age.  They live until someone kills them.  The Terran Ageless are much the same.  That is what makes them all good partners.