ExtensionDiscovery::getProfileDirectories() explicitly skips parent installation profile in installer, defeating its purpose

Problem

• ExtensionDiscovery::getProfileDirectories() explicitly skips the simpletest parent installation profile processing in the installer, which seemingly defeats the entire purpose of that environment value:

  <?php
       // For SimpleTest to be able to test modules packaged together with a
       // distribution we need to include the profile of the parent site (in
       // which test runs are triggered).
       // @todo !drupal_installation_attempted() defeats the whole purpose?
       if (drupal_valid_test_ua() && !drupal_installation_attempted()) {
         $testing_profile = \Drupal::config('simpletest.settings')->get('parent_profile');
  ?>

  
  (Note the code comment.)
• This means that additional modules that may be provided by an installation profile are not actually discovered when Drupal is installed in a web test.