The "superiority" of X86 had nothing to do with the demise/back burnering of other architectures.
Just about every processor arch has been maimed by confrontation on a marketing front... Alpha, Sparc, Power, Arm.... the ones that have survived have regulated themselves to niche markets (in the case of ARM a really really big niche) so they don't have to do battle with Intel and AMDs marketing and established user base.
I don't know about the rest but Sparc has backward compatibility that rivals Intel's as well as good performance.