Their logic was that it "squares off" the storage space, giving you a neat rectangle for all your suitcases etc. while also giving you somewhere to put stuff that you don't normally need access to, or which "perhaps" is valuable but needed to be stored out of sight.. But nobody puts stuff in there, because it's usually easier to just put occasional stuff under the floor. "Ze German mind is very tidy."
The S211 "boot" is quite long, so "maybe" it also just makes things a tad more accessible.
Plenty of these things will be found on EBay and breakers, essentially worthless because they're only useful in an S211 and they're too bulky and expensive to post. Someone may "ask" £50 but they won't get it. So just find one locally and put in a cheeky offer to take it off their hands.