I know some of the effort is just inadequate driver support - the various modes can't be turned on properly because they're locked behind proprietary blobs which need to be reverse engineered.
But is their something else? What's the pathology that leads to issues in software?
Power saving is all about racing towards that sweet idle state where every chip is clocked down and nothing radiates.
Which means that good power saving requires full vetting of every process on the system and making sure they all cooperate or, at least, are forced to sleep.
Android needed years to get into that state and developers/hackers are still sour about the restrictions it puts on them to keep battery life in check.
True. In my experience, many desktop applications do not care about minimizing idle cycles or network activity. So you end up with your radios always active, or some persistent CPU activity. For example, if one were to use Element Desktop, Signal Desktop and Discord simultaneously on PPP (all electron apps), we're looking at ~20% CPU utilization, idle!
Mobile Linux will get there eventually!
For reference, macOS introduced some APIs intended to improve power management around 2016 when the fanless usb-c MacBook Air came out.
I think this sort of thing is probably more effective than many believe at helping curb lackadaisical attitudes towards resource consumption among devs, with how it turns users into squeaky wheels.
I think Gnome has been taking starting steps - around Gnome 43/44 IIRC it started listing 'background apps' in the upper right pop menu.