Running the Dark Citadel is subjectively fun (depending if you like group play or not, it isn’t for everybody). It could very well be a weekly raid to run with a clan however the issue is that there’s no incentive to run it. As far as tangible rewards there aren’t any. The gear drops/mats/XP earned from this content is terrible/time & effort spent running the content. It would be more rewarding to run NMDs than to do Dark Citadel if you were trying to min-max your character.
The intended incentive for Dark Citadel were the cosmetics however they never drop. After chain killing the bosses 50 times, I never completed my set. And weapons seldom drop if at all. The only deterministic way to get cosmetics is to run the content and save up the ‘Citadel Coins’ and buy weapon skin form the vendor, however the vendor doesn’t sell every skin and nor does she refresh her goods every week on a rotation. Once we buy all the skins from her then the citadel coins become useless and there’s no reason to run Dark Citadel. This is the same reason why PvP is dead. Unless you want to casually duel there’s no reason to farm the fields of hatred. The PvP vendor has nothing to sell me. No reason to farm the coins for nothing to buy.