I believe the problem is that apple has stuck with LPDDR memory for performance (33% more memory bandwidth keeps integrated GPUs happy) and to hit power/efficie

I believe the problem is that apple has stuck with LPDDR memory for performance (33% more memory bandwidth keeps integrated GPUs happy) and to hit power/efficiency targets (variable frequency). Instead of a DIMM, LPDDR basically puts an entire DIMM on one chip soldered to the board (or package on the M1). LPDDR topologies tend to be limited in how many ranks of memory you can have, which limits the total capacity. I think if Apple really wanted to mac a "HEDT SoC", they would switch to "quad channel" (256bit wide) memory, which along with the jump to LPDDR5 would let them sell 64GB/128GB machines. The only existing SoCs with wide memory controllers is the Tegra Xavier though.