Changing Y Value in Vertex Array?

I was working from a tutorial on procedural mesh generation, and I decided to try something out. I wanted to go through the array of points that I had created and make their Y values all 1. However, the program didn't really seem to do anything. Here's the program:

 public class ProceduralMesh : MonoBehaviour {
 
     Mesh mesh;
 
     Vector3[] vertices;
     int[] triangles;
 
     void Awake () {
         mesh = GetComponent<MeshFilter>().mesh;
     }
 
     // Use this for initialization
     void Start () {
         MakeMeshData();
         CreateMesh();
 
         for (int i = 0; i < vertices.Length; i++)
         {
             vertices[i].y = 1;
         }
     }
     
     // Update is called once per frame
     void MakeMeshData () {
         //Create array of verts
         vertices = new Vector3[] {new Vector3 (0, 0, 0), new Vector3 (0, 0, 1), new Vector3 (1, 0, 0), new Vector3 (1, 0, 1)};
         //Create array of ints
         triangles = new int[] {0, 1, 2, 2, 1, 3};
     }
 
     void CreateMesh () {
         mesh.Clear();
         mesh.vertices = vertices;
         mesh.triangles = triangles;
 
         mesh.RecalculateNormals();
     }
 }

The for loop is what I was using to make it go through the list. Basically, the mesh just stayed at y = 0. It's probably something super simple, but all help would be gratefully received:)