This is my recollection of the era as well. A quality PC like a Compaq was already a good alternative during the Motorola era. In a lot of ways the whole RISC thing was a dead end as all that happened was SGI, IBM, HP and Sun cannibalised each others sales.
ARM is the only one left standing from that era which with hindsight seemed so unlikely.
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.
I think it would be more accurate to say the RISC workstation built entirely of custom low volume components was a dead end. Even if SGI decided to cut their margins to compete on cost their lowest prices would still be way above a PC workstation. Compaq benefitted from economies of scale that SGI could not.
RISC architectures live on today. Your house likely has dozens of MIPS chips in various components. You've got more ARM chips for sure but no shortage of other RISC chips in various components.
“Custom low volume components” is a marketing strategy. They could sell them to competitors and make money off the components. Late in its history SGI owned MIPS and sold their hardware to others. I have a WindowsCE laptop running on a MIPS R4000 processor. Runs NetBSD with effort, but with dignity.
ARM is the only one left standing from that era which with hindsight seemed so unlikely.