Because Windows stopped using s3 sleep. Testing and ensuring that s3 sleep works is a cost for laptop makers, and the number of Linux users is apparently not enough to justify it.
> Testing and ensuring that s3 sleep works is a cost for laptop makers
s/laptop makers/CPU vendors/
Reportedly neither Intel nor AMD are willing to support you if you’re developing firmware with S3 support for a platform using their recent CPUs (I believe that means ≥ 13th gen resp. ≥ Zen 4 but I’m not sure).
I don't understand why all vendors are actively trying to kill S3 sleep. It doesn't make any sense.