Arm came up with a bunch of standardisation requirements quite a while ago (see: https://developer.arm.com/architectures/system-architectures...) which have been quite successful especially for server designs.
That was an absolute requirement in order for AArch64 to even be considered as an alternative in the datacenter space where it is now a very compelling alternative to x86_64.
What I mean specifically is standardised support for firmware, hypervisor and operating system kernel interfaces for things like system bootstrap, power-perf control etc. Think ACPI, EFI, CPU capability discovery, DVFS, Idle management etc.
Being unable to boot Linux on modern AArch64 server class hardware is actually increasingly rare thanks to the standardisation.
Your comments are more applicable to the general Arm embedded systems scene where fragmentation is understandably rife. It was the price Arm had to pay to keep its royalty model in flight - "Pay the license fee, do what you will with the design".