Laravel: Custom Middleware is applying on each route

I created a middleware as:

use Closure;
use Gate;
class ACLMiddleware
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        if (Gate::denies('access-post')) {
            abort(403,'Not allowed!!!');
        }
        return $next($request);
    }
}

And then define in route as:

Route::get('/', 'HomeController@index');

Route::group(['middleware' => 'auth','acl'], function () {

    Route::resource('post', 'PostController');
   ...

When I run this.. it's applying on all routes, even on /. Why is like that?

via Chebli Mohamed