Javascript React useReducer使用fetch请求后，dispatch不会重新渲染组件

在这里，我在删除任务后通过react useReducer更新状态.我通过fetch API发送DELETE个请求，并在回调函数的末尾发送一个更新状态的操作.但状态不会更新.

const deleteTask = async (event) => {
    event.preventDefault();
    console.log("delete task");
    await fetch("http://localhost:3001/", {
      method: "DELETE",
      mode: "cors",
      headers: {
        "Content-type": "application/json",
      },
      body: JSON.stringify({ _id: state.task._id }),
    });
    dispatch({ type: "deleteTask", task: undefined });
  };

但当我按如下方式更改代码时:

const deleteTask = async (event) => {
    event.preventDefault();
    dispatch({ type: "deleteTask", task: undefined });
    console.log("delete task");
    await fetch("http://localhost:3001/", {
      method: "DELETE",
      mode: "cors",
      headers: {
        "Content-type": "application/json",
      },
      body: JSON.stringify({ _id: state.task._id }),
    });
  };

重新渲染发生，即状态被更新.谁能告诉我为什么会发生这种事？

这是我的delete减速器功能.

else if (action.type === "deleteTask") {
    return {
      ...state,
      isEditing: !state.isEditing,
      task: action.task,
    };
  }