There's a big difference in support for RISC-V and for, say, POWER (which has new processors in the line), Sparc, or Loongson (which is a new family of processors with roots in MIPS) which are all based around open architectures. You can restate the idea of Turing equivalence all you want, but that alone does not explain why one processor captures a bunch of human effort around it while others do not.
Part of that I think is Patterson and Hennessy writing one of the most standard books in the field and then turning it into its own ISA, which has in fact taken decades of their effort.
LLVM is a great tool, yes. There's a bigger body of research now than in 1985 or so, of course. But we had pcode before we had LLVM IR, and we had compile-to-C for a lot of languages in between. If you really think the only difference is some Kurzweilian inevitable march toward technological perfection over time and it has nothing to do with the tools being open and of high quality then I don't know what to tell you to dissuade you from that faith.