I've got a datapack where players can catch custom fish

{
    "type": "minecraft:fishing",
    "pools": [
      {
        "rolls": 1.0,
        "bonus_rolls": 0.0,
        "entries": [
          {
          "type": "minecraft:item",
          "functions": [
            {"function": "minecraft:set_nbt",
            "tag": "{CustomModelData:28}"},
            {
              "function": "set_name",
              "name": {
                    "text": "Flounder",
            "italic":"false"
                }
            },
            {
              "function": "minecraft:set_count",
              "count": 1
            }
          ],
          "name": "minecraft:tropical_fish",
          "weight": 10
        }
        ]
      }
    ]
  }

and sell them to a villager for items

/summon villager ~ ~ ~ {NoAI:1b,Willing:0b,VillagerData:{profession:"minecraft:fisherman"},Offers:{Recipes:[{rewardExp:0b,buy:{id:"minecraft:tropical_fish",Count:1b,tag:{CustomModelData:28,display:{Name:'{"text":"Flounder","italic":"false"}'}}},sell:{id:"minecraft:green_concrete",Count:1b}},{rewardExp:0b,buy:{id:"minecraft:tropical_fish",Count:1b},sell:{id:"minecraft:smoker",Count:1b}}]}}

Yet when I try to sell my custom fish to the villager, they don't accept the custom trade and instead get mistaken as a regular tropical fish. Is there something I'm overlooking?