I can't remember the reason given for that, but I too found that to be absolutely ridiculous too. It would have been nice if some effort had been made to make the layout a little more user friendly at least! The standard of the work was pretty poorly done too, with the floor and wall panels not matching either (no doubt awaiting the long overdue refurbishment / refreshment).
As an aside, I did a trip up to Reading recently and had two different 3 car 165s. I noticed in both, that the large 166 luggage racks have now been installed in the saloons, somewhat amusingly, with new FGW Carpet.