This is also about developer frustration, but not only. Over the years, I've used various alarm clock apps. There were some Huawei phones where it was literally impossible to get those alarm clock apps to work, because even if you added it to all whitelists, it would still kill the app in the background. Another issue is if you're using a messenger with VoIP functionality that you don't use every day. When an incoming call is received after not using the app for a while, it simply wouldn't ring.

Stock Android already contains energy saving mechanisms that work reasonably well. By piling potentially broken additional battery saving mechanisms on top of that, you risk breaking the phone for certain use cases. At the very least, as a user of that phone, there should be an easy way to exclude certain apps from energy saving measures. (Let's pick out Huawei again, where even if you added an app to such exclusion lists, after a few days the OS would randomly remove the app from that exclusion list again. Plus, there was some kind of "lock" that you could activate in the app switcher, but that lock wouldn't survive a reboot.)

Because some of the energy saving measures are so extreme, some manufacturers put popular apps on internal exclusion lists. These apps work fine, but apps by smaller developers don't. This is a major source of market distortion.

Huawei used to be the worst offender in this space, but it has gotten a little bit better by now. Nokia also had a phase where they had a horribly broken energy saver, but thankfully they got rid of that. Samsung has gotten worse and worse over the last years.