Why does customize_register only load inside of functions.php for me?

Question

I'd like to better understand - when I place the below into my functions.php file:

    add_action('customize_register', 'boat_annualReport_customize_register');
   function boat_annualReport_customize_register($wp_customize) {
      
      $wp_customize->add_section('boat-annualreport-callout', array ('title' => 'Annual Reports',
      // 'priority' => 1,
      //  'default' => 'testing',
       'title' => __('Annual Report', 'boat')
   ));

   $wp_customize->add_setting('boat-annualreport-callout-headline', array(
      'default' => 'Annual Report'
      ));
      
      $wp_customize->add_control( new WP_Customize_Control($wp_customize, 'boat-annualreport-callout-headline-control', array (
      'label' => 'Text',
      'section' => 'boat-annualreport-callout',
      'settings' => 'boat-annualreport-callout-headline',
      'type' => 'textarea',
      // 'active_callback' => 'boat_annualreport_callout_image_on_condition',
      )));

      $wp_customize->add_setting('boat-annualreport-callout-image', array(
      'type' => 'theme_mod', // or 'option'
      'capability' => 'edit_theme_options',
      'transport' => 'refresh',
      'sanitize_callback' => '',
      'sanitize_js_callback' => '' // Basically to_json.
      ));
      
      $wp_customize->add_control( new WP_Customize_Cropped_Image_Control($wp_customize, 'boat-annualreport-callout-image', array (
      'label' => 'Hero Image',
      'section' => 'boat-annualreport-callout',
      'settings' => 'boat-annualreport-callout-image',
      'type' => 'image',
      // 'active_callback' => 'boat_annualreport_callout_image_on_condition',
      'height' => 590,
      'width' => 1920
      )));
   }

It loads in the wp-admin customize section perfectly.

But when I place the code above from my functions.php file into my annualReportFunctions.php file and then modify my functions.php to the code below it does not load the custom_register function in the annualReportFunctions.php file. It does open the annualReportFunctions.php file, and it will fire other functions in it - but it will not fire any custom_register functions.

Please help me understand this. My functions.php file is going to be huge if I have to include every pages functions into one file - I would like to be able to split them up to load as needed :/

function boatTheBusForOutdoorAccess_register_scripts() {

   global $stringTmp;
   global $themeIncPath;
   echo $stringTmp;

   if ( $stringTmp === "" ) {
      require_once dirname( __FILE__ ) . '/inc/homeFunctions.php';
      // boat_homehero_customize_register($wp_customize);

   } elseif ( $stringTmp === 'find-your-trip' ) {
      require_once dirname( __FILE__ ) . '/inc/findYourTripFunctions.php';
      
      } elseif ( $stringTmp === 'who-we-are' ) {
         require_once dirname( __FILE__ ) . '/inc/whoWeAreFunctions.php';
      
      } elseif ( $stringTmp === 'what-we-do' ) {
         require_once dirname( __FILE__ ) . '/inc/whatWeDoFunctions.php';
      
      } elseif ( $stringTmp === 'support-our-mission' ) {
         require_once dirname( __FILE__ ) . '/inc/supportOurMissionFunctions.php';
      
      } elseif ( $stringTmp === 'plan-a-trip' ) {
         require_once dirname( __FILE__ ) . '/inc/planATripFunctions.php';
      
      } elseif ( $stringTmp === 'annual-report' ) {
         echo " 1";
         // global $stringTmp;
         require_once dirname( __FILE__ ) . '/inc/annualReportFunctions.php';
         echo " 4";      
      } else {
         echo "Page template slug is not an array or is not set.";
      }
   }

   
function boatTheBusForOutdoorAccess_register_url() {
   global $url;
   global $path;
   global $stringTmp;
   global $wp;

   if (isset($url) && is_array($url)) {
      echo " First hooray. This is an array and it is set ";

      $stringTmp = implode($url);
      $path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);
      $stringTmp = basename($path, ".php");  // Will remove `.php` suffix
   }
   boatTheBusForOutdoorAccess_register_scripts();
}
add_action( 'wp_enqueue_scripts',  'boatTheBusForOutdoorAccess_register_url');

Answer 1

In the second version you're running your code as a wp_enqueue_scripts hook. This is for frontend scripts and isn't called in the admin site. For that you need to hook admin_enqueue_scripts as well:

add_action( 'wp_enqueue_scripts', 'boatTheBusForOutdoorAccess_register_url');
add_action( 'admin_enqueue_scripts', 'boatTheBusForOutdoorAccess_register_url');

That said, it might be simpler to just include your admin scripts based on is_admin()

if ( is_admin() && ! wp_doing_ajax() ) {
    require_once dirname( __FILE__ ) . '/inc/annualReportFunctions.php';
}

It looks like you're trying to only load page-specific PHP on the right pages: I don't know how much that would really help (I think modern PHP runtimes have opcode caches etc.) but for the admin site at least I don't think it's worth worrying about and you might as well load all admin functions always there.

(Also note that you can use __DIR__ for the path: dirname( __FILE__ ) is for compatibility with old PHPs that WordPress no longer supports anyway.)