I doubt you'd get linear scaling of price/capacity - the larger capacity modules are more expensive per GB than smaller ones, and in some cases are supply constrained.

The number of chips on the bus is usually pretty low (1 or 2 of them on most GPUs), so GPUs tend to have to scale out their memory bus widths to get to higher capacity. That's expensive and takes up die space, and for the conventional case (games) isn't generally needed on low end cards.

What really needs to happen is someone needs to make some "system seller" game that is incredibly popular and requires like 48GB of memory on the GPU to build demand. But then you have a chicken/egg problem.

Example: https://wccftech.com/nvidia-geforce-rtx-5090-128-gb-memory-g...