Why is the view from my XIB file not being loaded by the UIViewController?

In my app delegate, I have:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
 {
     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     // Override point for customization after application launch.
     self.viewController = [[CGMContainerViewController alloc] init];
     self.window.rootViewController = self.viewController;
     self.window.backgroundColor = [UIColor whiteColor];
     [self.window makeKeyAndVisible];
     return YES;
 }
 

I have an unmodified CGMContainerViewController.h/m and a modified CGMContainerViewController.xib (added a button). The view is linked to the File Owner.

Why is the view from the XIB not showing?

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