Each of the five Necrolord houses of Maldraxxus possess at least one necropolis. Several of the structures appear to serve as the personal command centers of the houses’ margraves
A hause can posesses several, actually; remember Darakka’s story? We saw 3 necropoli of the Hause of Eyes
The Primus was personally involved in the design of at least one necropolis, the Zerekriss, which he shaped with his bare hands. Prior to his disappearance, he maintained a network of portals that linked the necropoli of Maldraxxus directly to the Seat of the Primus. The anima drought and the recent destruction of many of the necropoli have rendered those connections inactive, however.
Named
Exoramas, House of Rituals
Nurakkir, House of Eyes
Vortrexxis, House of the Chosen
Zerekriss, floats around Maldraxxus
Zolramus, Bastion (House of Constructs)
Unnamed necropolis in Plaguefall
They simply built it/have it before the draught and ordred it to go to Bastion
Remember, Maldraxxus suposed to be the bulwark of the Shadowlands, its shield and sword and tho its depicted ‘small’ the realm - Like every other - Is huge, not a continent, more like world sized.
A necropolis the equvivalent of a S.H.I.E.L.D. Helicarrier, Executor-class Super Stardestroyer or if you want real life examples, the ‘super’ battleship Yamato or USS Enterprise
Building one requires energy/anima, resources and operating it needs a trained crew and maldraxxus is not in the position to mass produce them, but had a nice ‘fleet’