Publish overload with notification of type object

The IMediator interface contains the following method:

Task Publish(object notification, CancellationToken cancellationToken = default);

In its implementation Mediator there is however a runtime type check if the argument notification implements INotification. Why does the interface allow object if callers are supposed to only pass instances which implement INotification?

[lilasquared]

If at compile time you can’t confirm that your object is of type INotification then you wouldn’t be able to use publish. Without the constraint you can

[oliverhanappi]

Is there any reason why I should not use one of the following?

if (message is INotification notification)
  await _mediator.Publish(notification);

or

await _mediator.Publish((INotification) message);