Why the function hook_form_alter doesn’t work on admin forms?

In my custom module .module file I implemented hook_form_alter thus: function my_module_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) { \Drupal::messenger()->addMessage(‘hook_form_alter found a form. It has the following name: ‘); \Drupal::messenger()->addMessage($form_id); } } When I go to the homepage of my drupal installation it correctly finds the search_block_form, but when I go to, for example, mysite/admin/config/system/site-information the function finds…