Fast-boot normally involves saving Windows to a swap partition and basically just half-hibernating. If that swap partition is shared with Linux it'd get overwritten and the boot method would swap to the slower one.
As far as I know there's no way to make a swap partition be exclusive to Linux or vice-versa.
Ramping up supply costs money, and the AI bubble is on the verge of popping. They'd need to know that this demand would be sticking around before investing in higher fab capacity.