It's nothing to do with the VRAM and all to do with the money, Nvidia want a bigger piece of the pie as the standard 3080 has an MSRP of £650 so the AIBs are getting the dies on the cheap and then doubling the cards price with most of that going into their pocket but now Nvidia says hang on a minute we'll have some of that so the add a few extra Cudas on and now the AIBs are paying Nvidia substantially more per die.It has become quite obvious that 10Gb is not enough for that tier of GPU. Some may disagree on this but when the manufacture decides to refresh their gpus to offer more then 10GB months before they release their next gen of gpus is a very telling sign that 10GB isn't enough. And that's on top of what was already discussed with titles at 4k, Texture Packs, etc.
The extra VRAM is just their to differentiate the cards as the dies are practically the same as the 3080 10gb.