AKCSHUALLY the M-series CPU memory upgrades are expensive because the memory is on-chip and the bandwidth is a lot bigger than on comparable PC hardware.
In some cases it's more cost effective to get M-series Mac Minis vs nVidia GPUs
They know that, but all accounts I've read acknowledge that the unified memory is worse than dedicated VRAM. It's just much better than running LLMs on CPU and the only way for a regular consumer to get to 64GB+ of graphical memory.
Still, I suppose that's better than what nvidia has on offer atm (even if a rack of gpus gives you much, much higher memory throughput).