Increase speed every 5 seconds

Why would this not work?

     public static float speed = -5f;
     public Vector2 obstacleVelocity = new Vector2(0.0f, speed);
     public Rigidbody2D rb;
 
     // Use this for initialization
     void Start()
     {
         InvokeRepeating("IncreaseSpeed", 3, 1);
         rb.velocity = obstacleVelocity;
         transform.position = new Vector3(Random.Range(transform.position.x - 2.2f, 2.2f), transform.position.y + 2, transform.position.z);
     }
     
     void Update()
     {
             
         Destroy(gameObject, 5);
     }
 
   
 
     void IncreaseSpeed()
     {
         speed = speed - 5f;
     }

I know there is a number of ways to do this, but what I tried to do is assign the Y value to -5, and then icrease Y (speed) every 3 seconds for -0.3f. It doesn´t seem to work, the objects are not getting any faster.

Thanks!