Why the variable updates only twice?

I have a script which controls an object in x direction. It also should give the direction of the object but the variable is only updated twice. If I move to the left in the log is written left if I move to the right after it is written right but if I move to the left again, nothing happens. Could anyone help?

    var speed = 1;
     static private var direction:String;
     
     function Update () {
         if(Input.GetKeyDown("left")){
             direction="left";
         }
     
         if(Input.GetKeyDown("right")){
             direction="right";
         }
     
         transform.Translate(Input.GetAxis("Horizontal")*speed*Time.deltaTime,0,0);
         print(direction);
     }