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?
Because of lack of standardised firmware on smartphone. PCs uses UEFI + ACPI to give information about devices to OS, on smartphone world different chip manufacturer have different bootloader and they load linux kernel and pass DT(device tree) which explains what devices are present and also smartphone were used to be less powerful, contains less storage (in past) so what they do is to compile linux with only the drivers which are actually present on that particular devices to save space. Thats why a smartphone rom is not a generics image which will run on all phone. But android/linux can be compiled like a generics image, look androidx86 project for example.
Also due to the windows, windows OS is closed source so device manufacture can’t simply modified it for their devices. They have to pass compatibility test which includes UEFI + ACPI compliant firmware to be present to be actually windows compatible (to get that sticker on their devices) without that microsoft will not provide windows licence to you i guess