I’m sorry if this sounds like a stupid question but why won’t android just straight up run like Linux distros that almost run on any computer? Why does each model under each manufacturers require separate maintainors seperately? Aren’t they running like almost similar hardware like processors from Qualcomm, mediatek, Exynos, etc? Why hasn’t there been a single android os that is compatible with all the device?
The issue is not the instruction set of the processors. That’s actually quite well standardised with ARM (albeit unfree) and there is plenty of generic support for it because of that.
The issue is all the “peripheral” devices such as WiFi, WWAN, display etc. that are wired up in extremely bespoke device-specific ways. They are usually implemented in vendor kernels with millions of lines of divergence to mainline at best and/or proprietary blobs at worst.
Changing the ISA from one well-supported closed standard to a less well-supported open one will not change that issue one bit.