Yes, thank you Captain Obvious. As you can see in my question above, I did not ask how they did it, I asked the purpose in doing it. The rationale for it being anonymous.
Their purpose in allowing it is to strenghten the advice and consent powers granted them by the constiution. IOW--it's not the senator but rather the senate that you should be all worked up about. They protect their own, for when the shoe is on the other foot.
Oh, and that's Admiral Obvious to you.