That "low-end" x86 machine still has an Intel/AMD chipset in addition to the processor, possibly a BIOS/UEFI chip from yet another vendor - they're substantiall

That "low-end" x86 machine still has an Intel/AMD chipset in addition to the processor, possibly a BIOS/UEFI chip from yet another vendor - they're substantially more difficult from a hardware standpoint to get going than any ARM MPU. Debug tools are inferior, as well. ARM MPUs became popular because they are actually easy to deploy.