Siege maps are just plain ugly
This is partly an aesthetic argument and partly a functional one that I think mirrors the 'tree acne' debate for field map design, but overall WH siege maps just have no design language whatsoever and that makes them look, feel, and work poorly - ugly, nonsensical, unimmersive, and confused. They feel like an abandoned set of a failed german expressionist film. And I dont think this is only applicable to 'human' settlements. Maybe the Skaven can get away with this. Fortress and cities are still built with some intention and design. If you remove the capture points from a WH map, you'd have a fairly difficult time really telling anything about the city itself.
The most recurring theme is that nothing exists in any context, and nothing relates to anything around it.
Picture 1: many assets are just... nonsense. They aren't any identifiable structure. Random slapped together bits of stone wall placed to fill a gap. It has no relationship with its surroundings. What is that even supposed to be?
Picture 2: This map is named "Altdorf" but of course the sheer dearth of actual maps means theres a lot of recycling. However, how many places would this map actually represent? Its in the middle of a mountain valley. The roads go nowhere. Theres no signs of life anywhere. Theres no exterior farms, or coaching houses, or watch towers, or anything. There is no residual sign of habitation or commerce or activity. How many city maps are riverine or coastal? How and why would you come here, and where would you go from here? Why would you be there at all? Its a pocket dimension. You can definitely have a coastal map even without an amphibious landing!
Picture 3: Theres very little notion that anybody actually lives here. Houses are placed at random and isolated.
Picture 4: If this is supposed to be some sort of isolated mountain fortress, why is the 'citadel' easily accessible, undefended, from the outside? That gap is larger than a gate, its hardly a postern door. Why is it there?
Picture 5: Overall, its hard not to get the impression that the sieges were designed in the same sloppy manner fields were. Asset acne was littered about to fill space and the roads were made around them.
Picture 6: The means of ingress/egress are also convoluted. In the bottom right - why would there be three gates clustered that close together? What do they serve? In some cases the exact same road, or a road that leads nowhere. In the top right, theres a gate approach without any towers. None of the roads from the gates really suggest that any location in the city is any more important than the other.
Picture 7-9: Cities in Attila. Relatively simple design language - its somewhere you would build a city, indeed. A prominent hill overlooking a plain, a river, a peninsula. Key locations are visible and distinct. You can tell what the major 'market square' is, or a temple, or a palace. Major avenues connect them in relatively simple and intuitive layout. Gates and roads are placed in a way that suggests some practical purpose (This is the gate you go through to get on the road going north, south, west, etc.) that gives it a relationship to its surrounding. The major avenues layout helps speak to which locations are important. This one goes to the central square, this one goes from the gate to the river, this one goes to the citadel. Houses are clustered in blocs, neighborhoods. Details evoke signs of life - market stalls, farms, upturned cabbage carts, etc. - even if there are no actual civilian sprites running around. You feel like you rolled up to besiege somewhere that actually exists in the context of the larger world.
I think you can reasonably extend this to most WH races. They'll all have 'major locations' in their cities they would privilege over others, and that they'd want to be able to move with relative ease in and out of. If they wanted to build an isolated mountain fortress, it would still have a coherent design language, identifiable roads to and from, citadels that are actually enclosed - see the last picture of Troy in Pharaoh as a pretty good example.