It has a lot more to do with physical space of the SODIMM slots, and in Apple's case the raw performance of on-die memory.
Re:In Defense of RAM
by throwaway49594 on Friday November 03, 2023 @01:07PM
(#38131713)
If you have talented engineers this is a solvable problem.
https://www.anandtech.com/show/21069/modular-lpddr-becomes-a...
That's very much the point of soldered-down RAM, isn't it? 64GB kit (2x32GB) of 260-pin (SO-DIMM) DDR4 modules show up around $110 on amazon. But why would manufacturer give customers such option, if they can be forced to buy whole new laptop instead?