> There's nothing inherently not-open about ARM, or at least it's no less open by nature than x86. The fact that most ARM devices are locked down is a secondary effect from most of them being phones.

I'd argue lack of something like ACPI to discover the device tree and memory map is why this impression exists. Besides the ARM CPUs not being socketed.

Exactly. There is no agreement on how the universal operating system should expect the generic ARM computer to boot and expose its hardware.