Why is it trying to grab the wrong rigidbody?

From my understanding, foreach loops through an array of objects; if no elements are present in that array it returns null.

Going off that information, I have a foreach loop that doesn't seem to be executing properly:

 void MovementControl() // Controls platform movement
     {
         Vector3 movementVector = new Vector3(0f, 0f, moveSpeed * Time.deltaTime);
         platformRigidbody.velocity = movementVector;        
 
         // Cycle through GameObject[] platforms and add a movement speed via force onto rigidbody        
         platforms = GameObject.FindGameObjectsWithTag("Platform");
         foreach(GameObject platform in platforms)
         {
             platformRigidbody = platform.GetComponent<Rigidbody>();
             platformRigidbody.velocity = movementVector;
             if(platform.transform.position.z > removePositionZ){ Destroy(gameObject); }
         }        
     } 

The above code should cycle through every GameObject, find the attached rigidbody and apply a movement vector onto it.

So, why does it try to grab the rigidbody from the Spawner?