Why aren't structures spawning in my flat world?

So im making a custom world and i added some structures, but they aren’t spawning. Only nether fortresses and bastions spawn. I tried changing setting, but they still don’t spawn (woodland mansions, ocean monuments, and end cities).
If i do /locate it crashes.

    {
  "type": {
    "name": "minecraft:test",
    "ultrawarm": false,
    "natural": false,
    "piglin_safe": false,
    "respawn_anchor_works": false,
    "bed_works": false,
    "has_raids": false,
    "has_skylight": false,
    "has_ceiling": false,
    "coordinate_scale": 1,
    "ambient_light": 0,
    "logical_height": 256,
    "effects": "minecraft:overworld",
    "infiniburn": "minecraft:infiniburn_overworld"
  },
  "generator": {
    "type": "minecraft:flat",
    "seed": -98454062,
    "settings": {
      "lakes": false,
      "features": false,
      "layers": [
        {
          "block": "minecraft:end_portal_frame",
          "height": 1
        },
        {
          "block": "minecraft:barrier",
          "height": 2
        },
        {
          "block": "minecraft:obsidian",
          "height": 1
        },
        {
          "block": "minecraft:blackstone",
          "height": 10
        },
        {
          "block": "minecraft:warped_hyphae",
          "height": 2
        },
        {
          "block": "minecraft:polished_blackstone",
          "height": 2
        },
        {
          "block": "minecraft:soul_sand",
          "height": 3
        },
        {
          "block": "minecraft:black_stained_glass",
          "height": 1
        }
      ],
      "structures": {
        "structures": {
          "minecraft:bastion_remnant": {
            "spacing": 10,
            "separation": 5,
            "salt": 0
          },
          "minecraft:endcity": {
            "spacing": 2,
            "separation": 1,
            "salt": 0
          },
          "minecraft:fortress": {
            "spacing": 10,
            "separation": 5,
            "salt": 0
          },
          "minecraft:mansion": {
            "spacing": 2,
            "separation": 1,
            "salt": 0
          },
          "minecraft:monument": {
            "spacing": 2,
            "separation": 1,
            "salt": 0
          }
        }
      }
    }
  }
}