Route::auth() just registers routes for you. You can register them yourself if you want different functionality.

If you looked into the Router you would see the routes that are added for you when calling Route::auth().

You can also change the layout yourself to remove that link, as you have.

The second part is you are responsible for your application and its routes. If you leave routes or links in your templates that shouldn't be there, that is on you.

You can easily see all your routes with a simple artisan route:list.

As with many things this is a helper for convenience. If you want something else or different functionality you don't have to use it at all.