How to assign objects to a class in C# (Unity)

Question

I have this code below. Why in my ReadFile is me logging (and also my file) saying the array is empty. I call readFile first and the file doesn't exist. Then I call writeFile and it writes an empty array. Sorry I am not great at c#.

public class GameData : MonoBehaviour
{

    string saveFile;
    CarsUnlocked[] carsUnlocked = new CarsUnlocked[3];

    void Awake()
    {
        saveFile = Application.persistentDataPath + "/gamedata.json";
        readFile();
    }

    public void readFile()
    {
        if (File.Exists(saveFile))
        {
            string fileContents = File.ReadAllText(saveFile);
            carsUnlocked = JsonUtility.FromJson<CarsUnlocked[]>(fileContents);
        } else {
            carsUnlocked[0] = new CarsUnlocked(1,2,3,true);
            carsUnlocked[1] = new CarsUnlocked(1,2,3,true);
        }
    }

    public void writeFile()
    {
        Debug.Log(carsUnlocked);
        string jsonString = JsonUtility.ToJson(carsUnlocked);
        File.WriteAllText(saveFile, jsonString);
    }
}


public class CarsUnlocked : MonoBehaviour
{
    public int car;
    public int levelNeeded;
    public int moneyNeeded;
    public bool unlocked = false;   

    public CarsUnlocked(int carX, int levelNeededX, int moneyNeededX, bool unlockedX)
    {
        car = carX;
        levelNeeded = levelNeededX;
        moneyNeeded = moneyNeededX;
        unlocked = unlockedX;
    }   
}