Apple deploys LPDDR5X for the energy efficiency and cost (lower is better), whereas NVIDIA will always prefer GDDR and HBM for performance and cost (higher is better).
The main OS needs to run somewhere. At least for now.
The justification is that processors cores aren't getting much faster, but what they are is getting more numerous - entry-level machines have between 4 and 8 cores - and adapting code to run across multiple cores is important if we want to utilise all those cores.
the core count doesn't matter. a top of the line Turin system has less than 1.4TB/s memory for the whole dual CPU system. A 2020 era A100 has 2TB/s.
with MGX and CX8 we see PCIe root moving to the NIC, which is very exciting.