Yes... for an individual, those are the prices (if only there was some 3 hour youtube video about adding more memory to cards...).
The issue is that even a downstream isn't buying 100 dollars of VRAM. They need to buy that in bulk. And then they need to retool their factories to support that configuration. And if they can't sell enough of those units to justify the retooling and the purchases?
I mean... look at EVGA
And then you have the marketing/brand implications which I already spoke to.