Ok so it seems some people are only relying on heroic deaths. There is a certain criteria for ghosts reviving dead people. It's said by the Speaker when he talked with Ghual. Devotion, Bravery, and sacrifice. That's also why Uldren was revived. He had devotion for his sister, bravery for embracing the darkness, and sacrifice for the sister he loves. This could also be found in the lore tab of.... was it pork meat? I forgot the name of Uldren's ghost, but it is a lore tab that describes the events prior to Uldren's second life. so, I don't see why people from ancient times won't be revived, but as long as they meet the criteria, then why not?