What is ACPI other than a DTB baked into the firmware/bootloader?

Any SBC could buy an extra flash chip and burn an outdated U-Boot with the manufacturer's DTB baked in. Then U-Boot would boot Linux, just like UEFI does, and Linux would read the firmware's fixed DTB, just like it reads x86 firmware's fixed ACPI tables.

But - cui bono?

You need drivers in your main OS either way. On x86 you are not generally relying on your EFI's drivers for storage, video or networking.

It's actually nice that you can go without, and have one less layer.