为什么params需要并且不允许传递值来创建新记录？

Question

我有以下内容：

class ArticlesController < ApplicationController
  before_action :find_article, only: [:edit, :update, :show, :delete]

  def create
    @article = Article.new

    if @article.save(article_params)
      flash[:notice] = "Successfully created article!"
      redirect_to article_path(@article)
    else
      flash[:alert] = "Error creating new article!"
      render :new
    end
  end

  private

  def article_params
    params.require(:article).permit(:title, :body)
  end

end

日志显示表单正确提交值：

Started POST "/articles" for ::1 at 2017-01-01 11:30:13 -0800
Processing by ArticlesController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"xx==", "article"=>{"title"=>"MAKEMEWORK", "body"=>""}, "commit"=>"Create Article"}
   (0.3ms)  BEGIN
  SQL (0.4ms)  INSERT INTO "articles" ("created_at", "updated_at") VALUES ($1, $2) RETURNING "id"  [["created_at", "2017-01-01 19:30:13.630647"], ["updated_at", "2017-01-01 19:30:13.630647"]]
   (0.5ms)  COMMIT
Redirected to http://localhost:3000/articles/7
Completed 302 Found in 15ms (ActiveRecord: 4.0ms)

但是，在日志中看到的标题值未在控制器中使用。知道为什么吗？