Yeah, I'm aware it's in the kernel, but it's only useful for PCs. So effectively it's a "desktop" problem in terms of people deciding to dedicate resources to it. And... hence why it breaks all the damn time.
My point is suspend states aren't important to big commercial users who are running linux servers. They have no reason to contribute to making it work well. Hence, it likely doesn't get much attention compared to many other parts of the kernel.
It doesn't have to do with "Desktop environments", but it very much is part of the "linux desktop" experience.