My low-end Canon DSLR from 2011 powers on and is ready to shoot in ~2 seconds. I can keep the camera turned on for hours at a time (with the screen off except while taking pictures) without any noticeable effect on the battery charge level. Can you imagine an Android-based camera body achieving something like that?
Abolutely. An android phone can last a week in airplane mode and a low power CPU state.
Zeiss are going to release a full-frame digital camera soon that runs Android [1][2]. The ZX1 also comes with a built-in version of Adobe Lightroom.
[1] https://www.theverge.com/circuitbreaker/2018/9/27/17911212/z...
[2] https://www.dpreview.com/news/3430444458/zeiss-announces-ful...
Samsung did this: https://www.dpreview.com/reviews/samsung-nx1 but gave up the market in 2015.
That was likely a good idea from a cost-benefit perspective, as standalone cameras continue to decline in unit volumes: https://www.dpreview.com/news/7719403699/cipa-s-november-num..., but it's a shame from a technological progress perspective. You are totally correct that a camera body really ought to be an Android device, but camera makers have not done that—which likely contributes to their fall in unit sales.