Because you also need SpriteRenderer to render your sprite.
void Start () {
Sprite mySprite = Sprite.Create(myTex, new Rect(0, 0, myTex.width, myTex.height), new Vector2(1, 1), 100);
GameObject myObj = new GameObject();
SpriteRenderer spriteRenderer = myObj.AddComponent<SpriteRenderer>();
spriteRenderer.sprite = mySprite;
}