Not to mention the 24GB of VRAM. Of course we don't need anywhere near this for gaming, but at 4K it's likely we will need more than 10GB, especially with newer games with higher texture options.
Besides, spending £850+ on a good 3080, and then worrying about how long 10GB will last you at 4K, is not good sense to me. I want to be completely happy with my purchase, knowing it's fully capable for the 4k games to be released over it's 2 year lifespan.
Also, sometimes you get a surprise in life. I bought my current Radeon VII for £630 on release day from OCUK. When I sell it, I'll actually make £100-200 profit, as the card is pretty much a MI50 - so they are highly desired on the bay and other places. Doubt that will happen with the 3090, but you never know.
The FX's of the world are likely on 720P monitors, and can't fathom why someone would need more than 10GB. Bless.