Wondering what's the practical use of this discussion? There are millions of issues like this in Airbus. You will freak out trying to find reasons behind all of them. Just follow the procedure. It was designed this way. To go through CBT, FTD, FFS and fly it next day with passengers. Sure, over time we come across usefull things. But in this case I don't think knowing the reason why the aircraft goes into Direct Law will help you in any way. To remember that it goes Direct? It's written in the QRH or on the screen!
We have so many other thing to know and remember.
Last edited by Romasik; 20th Feb 2017 at 15:01.