Maybe they bought them for something else and had nowhere to use them knowing how things were run 
I had C128 , it should have had built in disk drive (that would probably need another CPU) at that point and a mouse.
Only good thing is that case looked much better and more professional.
The c128dcr had a built in 71, Both commodore and CMD made mice for the c64/128
Lt Kernel(SP?) and CMD made hard drives.
The z80 was chosen on purpose not for just cpm, but it was a necessary chip to make all 3 modes live together,iirc it used the z80 for its early startup.
