Hidden dependencies - why not?

Hidden dependencies:

function __construct($dep_registry){
  $this->db = $dep_registry->get('db');
  $this->request = $dep_registry->get('request');
  ...
}

Not so hidden:

function __construct(Db $db, Request $request, ....){
  $this->db = $db;
  $this->request= $request;
  ...
}

The disadvantages of the last is that, if I need to change the class later and need another dependency, I have to change the constructor arguments. And if I change the constructor, I need to also change every file that uses it. With hidden deps the change would only be needed in the two places: the constructor and the registry class. Another fail of the 2nd method is that it's not possible to lazy load dependencies, i always have to pass the instances

So what's the disadvantage of hidden deps and why is it bigger than this disadvantage of not so hidden deps?