alt Hacker NewsLike others have said, it comes down to apps mostly. But there is also the fact that Google and others have spent more than a decade optimizing the OS for appliances. Android was built from the ground up for mobile devices and handles things like background apps, notifications, and charging as expected on a phone. All of this could be ported or rebuilt, but the work has already been done for Android and billions of devices prove that it works.
AOSP even with the GrapheneOS improvements provides far better privacy and security than a desktop distribution. Those are the hardest things for a desktop OS to accomplish since they cannot force the whole software ecosystem to conform and very few developers care about it. Developers largely treat their own code and dependencies as trusted. Few developers are inclined to heavily invest resources in limiting their own access and capabilities. The baseline sandbox provided by AOSP enables the GrapheneOS improvements because of how much is standard.
https://news.ycombinator.com/item?id=49364220