Issue with the c# script for player climb in unity

I am trying to make the player to climb a ladder. (2D game)

I used this code for that,

 void OnTriggerEnter2D(Collider2D collider){
     if(collider.gameObject.tag=="Ladder"){
         _canClimb = true;
         _anim.SetBool("Climb",true);
     }
 }
 
 void OnTriggerExit2D(Collider2D collider){
     if(collider.gameObject.tag=="Ladder"){
         _canClimb = false;
         _anim.SetBool("Climb",false);
     }
 }

In the update() ,

 if(Input.GetKey(KeyCode.UpArrow) && _canClimb == true){
     transform.position = Vector3.Lerp(transform.position,ladderTop.transform.position,Time.deltaTime);
 }

I have put a child game object to ladder to get the position of the top of the ladder.

But When the player jumps and hit with the box collider of the ladder I can see the climbing animation. And after that the player falls down to the ground again. It doesn't move up. What is the reason for that?