Why is -content-add-list.html.twig template not being used?

I have generated a custom content entity via the Drupal Console. It has bundles. I would like to customise the screen which you get to when adding a new such entity - the screen which displays the list of bundles, to click on the type you want to add.

When I generated the entity, a bunch of template files were created, including one called <my_entity>-content-add-list.html.twig. I am certain this is intended to override the core template called entity-add-list-html.twig. However, changes I make to it do not take effect, and by putting twig in debug mode and viewing the source, I can see that it is not being overridden.

Do I need to add a theme suggestion hook? If so, what would the name of the function be? I feel like I must be missing something. Given that the console generated that template I am surprised it is not automatically used. But surely there must be a simple way of telling Drupal to use it.

EDIT: I've found what to name the function: it's mymodule_theme_suggestions_entity_add_list. But the machine name of the entity is nowhere in the $variables array that I can easily get at. I'm looking at parsing the route to get it out, which seems rather hacky

So I got there in the end (the machine name of the entity being oc_activity:

function opencase_entities_theme_suggestions_entity_add_list(array $variables) {
  $route_name = \Drupal::routeMatch()->getRouteName();
  $suggestions = []; 
  if ($route_name == "entity.oc_activity.add_page") {
    $suggestions[] = 'oc_activity_content_add_list';
  }
  return $suggestions;
}

But it feels too hacky & hard-coded; it seems there ought to be a nicer way.

Also, the template file that was generate by the console assumed that the array of bundles was called types when actually it was bundles. So I had to change the generated code from for type in types to for type in bundles. Just putting that here in case it's useful to anyone...