Unlike strongholds which are very diverse, the nether fortress exclusively generates using pristine nether brick and fence. This makes the nether fortress appear bland and newly constructed. This is inconsistent with every other structure in the game which use at least a few varients of the block in which they are made.
To name a few:
Dungeon - Cobblestone and Mossy Cobblestone
Pyramid - Sandstone, Cut Sandstone, and Chiseled Sandstone
Ocean Monument - Prismarine, Prismarine Bricks, and Dark Prismarine