Keep in mind several of the others survived long past their public visibility. There were MIPS smart phones for a while. Both PPC and MIPS long outsold x86 in number of CPUs - just at low margin licenses with the bulk going into embedded uses, like ARM.
ARM had the advantage in that space of starting from the very low end, and being able to squeeze margins instead of being squeezed.
Don't forget IBM is still selling (and improving) their POWER family, running AIX (which had the low-end eaten away by Linux) and IBMi (which is the only minicomputer family still standing). IBMi is extremely well defended as it's not even fully documented (unlike mainframes) and, therefore, doesn't even have a way to be emulated outside IBM. And I would not be surprised if that "secret sauce" to be kept in an underground facility under a mountain in the middle of a desert, in a completely offline system behind multiple biometric locks.
ARM survived this long because it had a niche others couldn't break into (and still can't) as the highest performance per watt anywhere.
ARM had the advantage in that space of starting from the very low end, and being able to squeeze margins instead of being squeezed.