Laravel使用attach添加数据时observer的created方法不执行是什么原因？

问题：

关注接口没有触发observer, 而评论接口触发了oberser, 两者区别是一个使用的attch方法，另一个使用时create方法，请问是否是attach方法的原因？如果是，为什么attach方法不能触发observer？代码如下

接口

// 关注接口
 public function follow(Post $post){
     // observer没有调用
    $post->follows()->attach(\Auth::id(), ['created_at'=>Carbon::now()]);
    return back()->with('success', '关注成功');
}

// 评论接口
public function comment(Request $request, Post $post){
    $this->validate($request, [
        'content' => 'required|string|min:4|max:256'
    ]);
    $comment = $request->all();
    $comment['post_id'] = $post->id;
    $comment['user_id'] = \Auth::id();
    // observer有调用
    $post->comments()->create($comment);
    return back()->with('success', '评论成功');
}

FollowObserver类

<?php

namespace App\Observers;

use App\Models\Follow;

class FollowObserver
{
    /**
     * Handle the follow "created" event.
     *
     * @param  \App\Models\Follow  $follow
     * @return void
     */
    public function created(Follow $follow)
    {
        $post = $follow->post();
        // post关注数+1
        $post->increment('follow_count');
    }
}

CommentObserver

<?php

namespace App\Observers;

use App\Models\Comment;
use App\Models\Post;
use Carbon\Carbon;

class CommentObserver
{
    /**
     * Handle the comment "created" event.
     *
     * @param  \App\Models\Comment  $comment
     * @return void
     */
    public function created(Comment $comment)
    {
        $post = $comment->post;
        // post的评论+1
        $post->increment('comment_count');
        // post的活跃时间更行
        $post->update(['updated_at'=> Carbon::now()]);
    }
}

ObserverServiceProvider

<?php

namespace App\Providers;

use App\Models\Comment;
use App\Models\Follow;
use App\Models\Post;
use App\Observers\CommentObserver;
use App\Observers\FollowObserver;
use Illuminate\Support\ServiceProvider;

class ObserverServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot()
    {
        //
        Comment::observe(CommentObserver::class);
        Follow::observe(FollowObserver::class);
    }

    /**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        //
    }
}