An actual technical answer: Apparently, it's because while the PS5 and Xbox Series X are technically regular x86-64 architecture, they have a design that allows the GPU and CPU to share a single pool of memory with no loss in performance. This makes it easy to allocate a shit load of RAM for the GPU to store textures very quickly, but it also means that as the games industry shifts from developing for the PS4/Xbox One X first (both of which have separate pools of memory for CPU & GPU) to the PS5/XSX first, VRAM requirements are spiking up because it's a lot easier to port to PC if you just keep the assumption that the GPU can handle storing 10-15 GB of texture data at once instead of needing to refactor your code to reduce VRAM usage.