Player Doesn't Die

private bool gameStarted = false;
[SerializeField]
private Text gameStateText;
[SerializeField]
private GameObject player;
[SerializeField]
private BirdMovement birdMovement;
[SerializeField]
private FollowCamera followCamera;
private float restartDelay = 3.5f;
private float restartTimer;
private PlayerMovement playerMovement;
private PlayerHealth playerHealth;

// Use this for initialization
void Start () {
    Cursor.visible = false;

    playerMovement = player.GetComponent<PlayerMovement> ();
    playerHealth = player.GetComponent<PlayerHealth> ();

    // Prevent player from moving
    playerMovement.enabled = false;

    // Prevent bird from moving
    birdMovement.enabled = false;

    // Prevent camera from moving to its game position
    followCamera.enabled = false;

}

// Update is called once per frame
void Update () {

    // If the game is not started and user presses the spacebar ... 
    if (gameStarted == false && Input.GetKeyUp (KeyCode.Space)) {

        // ... start the game
        StartGame ();
    }

    // If the player is no longer alive .. 
    if (playerHealth.alive == false) {

        // ... end the game
        EndGame ();

        // increment a timer to count up to restarting
        restartTimer = restartTimer + Time.deltaTime;

        // ... if it reaches the restart delay
        if (restartTimer >= restartDelay) {

            // ... reload currently loaded scene
            SceneManager.LoadScene (SceneManager.GetActiveScene().buildIndex);
        }

    }
}

// Start the game
private void StartGame () {

    // Set game state
    gameStarted = true;

    // Remove the start text
    gameStateText.color = Color.clear;

    // Enable movement
    playerMovement.enabled = true;
    birdMovement.enabled = true;
    followCamera.enabled = true;

}

// End the game
private void EndGame () {

    // Set game state
    gameStarted = false;

    // Show the GAME OVER text
    gameStateText.color = Color.red;
    gameStateText.text = "GAME OVER";

    // Remove the player from the game
    player.SetActive (false);

}