They probably literally don't have enough NAND to go around. 768GB of memory (48GB x 16) is enough for nearly 100 iPhone 17s; that's $80k (corrected) of iPhones at MSRP, although likely much lower margins than these high-RAM boxes.
They also cancelled availability of the 512 M3 Ultra months ago in many regions, likely just redirecting memory
800 USD/iPhone x 100 iPhones = 80k USD
They also cancelled availability of the 512 M3 Ultra months ago in many regions, likely just redirecting memory