>Then why did their refresh flop this year?
Not only it didn't, they will get even more stuff soon with Corsair expansion
>Why were they not launch factions for Gladius?
So they could be sold as a dlc. Cool stuff you need to always leave for dlcs.
>Why are they not in Battlesector after years of DLC?
Why not? Other factions got in first
>Why were they passed over for a BFGA2 campaign in favor of Necrons and Nids?
As the faction with the biggest variety next to Imperium, they were left for a potential DLC. Dev was forced to abandon game only after releasing disliked Chaos campaign.
>Why do they have not one, but TWO cancelled book series?
CEO change and scrapped plans to remove Slaanesh, on top of Eldarfags disliking Ynnari anyway
>Why have they not been feature in a significant narrative in almost ten years?
Good guy faction slot is always occupied as the Marines. Only bad guys can become edition villains. Good guy factions like Tau, Votann and Eldar won't ever get into starting box for this same reason.
>Why does killing them off in Rogue Trader actually IMPROVE the plot?
It doesn't