Probably cause the Nightmares appeared in this game recently
Wait what's so fair about having a collector's card. It's not a privlege, it's to cycle out older cards, to powerful cards or perhaps even cards that just weren't used to add interest. Newer clans shouldn't have collectors as it makes little sense, they haven't even gotten to circulate. I somehow wouldn't be suprised if you wanted that to happen since you have all the Nightmare cards and are looking to make some big sells. I believe let the staff decide when and if a card should go collector, not just force every clan to have a collector as that makes them all uniform in that respect.
And what does that matter about collectors? My amount of cards and seeing collectors being made just to make them don't have anything to do with each other. I just don't see the point of making all the clans have a collector right away especially allstars which isn't even finished. As if they already had a collector said collector would be rarely seen or used, taking away from the game.
I am sure it will eventually have one just Nightmare is one of the newer clans. Sentinel and Geist are just getting their first collectors now. Nightmare will likely get one someday just be patient. While in my opinion more collector cards are not really needed as it limits the use the card will get I am sure eventually all clans will have one or two.