Variable Scope

Why is it that my variable "attack" has a scope that extends into the "Attack()" function, but my variable "target"'s scope does not reach into the "GetTarget()" function? Just curious.

 using UnityEngine;
 using System.Collections;
 
 public class MonsterAI : MonoBehaviour
 {
     public string name = "NoName";
     public GameObject target = null;
     public float hp = 100f;
     public float attack = 10f;
     public float speed = 100f;
     public float team = 1f;
     
     public float action_bar = 0f;
     
     void Start()
     {
     
     }
     
 
     void Update()
     {
         //ticking down their action bar
         if (action_bar < 100f)
         {
             action_bar += speed * Time.deltaTime;
         }
         else
         {
             target = GetTarget ();
             Attack ();
             Debug.Log (name + " has ended their turn.");
             target = null;
             action_bar = 0f;
         }
         
         //death
         if (hp <= 0)
         {
             Destroy (gameObject);
         }
     }
     
     //functions
     GameObject GetTarget()
     {
         GameObject[] target = GameObject.FindGameObjectsWithTag("Monster");
         return (target[0]);
     }
     
     void Attack()
     {
         string target_name = target.GetComponent<MonsterAI>().name;
         float damage = Mathf.Round(Random.Range (attack - (attack * .1f), attack + (attack * .1f)));
         target.GetComponent<MonsterAI>().hp -= damage;
         Debug.Log (name + " attacks " + target_name + " for " + damage + "damage.");
     }
     
     void Dodge()
     {
         
     }
 }