While I don't have an exact answer, we can speculate:Ehhh, why is DDR5-4800 CAS 40 when DDR4-4800 is CAS 19?
That's going to negate all (or more) of the various other architectural performance improvements of DDR5.
Probably logistics. It's easier to mass produce one item than two.WTF, why is there a double height PCB for only 8 DRAM packages?
Why are you wasting so much PCB when you could've easily packaged it on smaller PCB?
If you look at only that part then you could make the argument. But the logistics concerning having multiple items could in the long run require more resources that it effectively offsets any material efficiency.But at the cost of Material Inefficiency which is bad for the environment.