Laravel Eloquent event not triggered when model is touched

Laravel 5.7. I have 2 models: Foo and Content:

class Foo extends Model
{
    public static function boot()
    {
        parent::boot();
        static::updated(function() { 
            dd('here');
        });
    }

    public function contents()
    {
        return $this->morphToMany('App\Content');
    }
}

class Content extends Model
{
    protected $touches = ['foos'];

    public function foos()
    {
        return $this->morphedByMany('App\Foo');
    }
}

When Content is updated, it correctly touches Foo, updating its updated_at timestamp. But the static::updated method is not called. I would expect it to be called since Foo has been updated.