If I remember correctly the pinout on these RAM modules was demonstrated to be substantially higher than any openly commercially available comparable module, and there is also the case of ridiculously low idle RAM consumption on M1/M2 machines.
This article has an image:
https://www.macrumors.com/2021/04/06/m1-mac-ram-and-ssd-upgrades-possible/
Looks to me like there are around 700-800 pins at least. Now compare it to usual modules one sees around.