You are obviously right on security aspect. Nevertheless, we can retrieve the private key on many platforms (F5, Microsoft, IHS, ...).
I don't know exactly what I want to do. Right now, it's only driven by individual curiosity.
Use case: The need to set up the same certificate on the LB VIP AND on the backend servers. (I can import the private key/certificate pair from the servers to the LB. Can I do it the other way around ?).