From what I read, it was a lot of the prosumer/gamer brands (MSI, Gigabyte, ASUS) implementing their part of sleep/hibernate badly on their motherboards. Which honestly lines up with my experience with them and other chips they use (in my case, USB controllers). Lots of RGB and maybe overclocking tech, but the cheapest power management and connectivity chips they can get (arguably what usually gets used the most by people).

Power management is a really hard problem. It's the stickiest of programming problems, a multi-threaded sequence where timing matters across threads (sometimes down to the ns). I'm convinced only devices that have hardware and software made by the same company (Apple, Andoid phones, Steam deck, maybe Surface laptops) have a shot in hell at getting it perfect. The long-tail/corner cases and testing is a nightmare.

As an example, if you have a mac, run "ioreg -w0 -p IOPower" and see all the drivers that have to interact with each other to do power management.

It never really worked in games even with S3 sleep. The new connected standby stuff created new issues but sleeping a laptop while gaming was a roulette wheel. SteamOS and the like actually work, like maybe 1/100 times I've run into an issue. Windows was 50/50.