quick question

why is my achievement not fully hidden?
code:
{
  "display": {
    "icon": {
      "id": "minecraft:saddle"
    },
    "title": "",
    "description": "",
    "show_toast": false,
    "announce_to_chat": false,
    "hidden": true
  },
  "criteria": {
    "has_leather": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [
          {},
          {
            "items": "minecraft:leather"
          }
        ]
      }
    }
  },
  "rewards": {
    "recipes": [
      "mounts_improved:saddle_recipe"
    ]
  }
}