Because they like to play to their following, which mostly consists of amd fans, which just so happen to be the most vocal thus more clicks/views for them (which is fair enough given they make their living from YT), vram is basically the only thing that amd have over the competing nvidia gpus hence why it is such a hot topic, look back at the fury x days and vram didn't matter at all
Hilarious though that, 3080 should be 20gb yet it's competing gpu only has 16gb of vram.... Especially when it's been shown that AMD GPUs aren't as efficient in their vram utilisation as Nvidia GPUs across several games
Ding ding, all the vram on rdna 2 and 3090 is doing jack **** given they still have to drop settings and use higher presets of dlss/fsr too and funniest thing is still the fact that well regarded broken games are used to score points as Alex stated

And best of all, as even stated by these sites like computerbase, pcgamershardware, they state that there are still even problems on the best of the best pc hardware.
The people who keep on going on about it being nvidias fault because of them being stingy on vram are the real problem for the pc gaming scene as they are accepting what is quite frankly obvious lazy/poor ports and thinking it is perfectly acceptable that the only way to max games out now is by spending ££££.....

But given most people don't work in the development industry, they have no clue how things actually work. Soon we'll have 4090/7900xtx owners upgrading to the 5090/8900xtx just to be able to hit 60+ fps with max settings in the next lot of titles....