Why does Slim practice such work with containers (with an example)?

Question

Slim Framework

For example, put the controller in a container

$container['UserController'] = function($container) {
  return new App\Controllers\UserController($container);
};

$app->get('/', 'UserController:listUsers');

Why, if it is possible so (that is, immediately call the desired method in the router)?

$app->get('/', 'App\Controllers\UserController:listUsers');