Why the 'request' key is not in the binding's array in the container when I dd(app())

Question

To my understanding, the 'request' key returned by the getFacadeAccessor method in the Request Facade, refers to the key bound in the service container in the bindings array.

And when I dd(app('request')) I get the Request object. However, when I dd(app()) I don't see the 'request' key in the bindings array. Why is this so?