hook_form_user_register_form_alter() does not customize user registration form
For all Drupal _alter hooks, you need to pass the variables you need to change as references. 

In your function, declaration, $form should be &amp;$form. This makes PHP pass a reference of that variable to inside if your function scope, so changes you make to the $form array persist.

So the function declaration should look like this (to alter both variables):
hook_form_user_register_form_alter(&amp;$form, &amp;$form_state)