You're assuming there is something inherent to Arm specifically that makes it efficient. I'm not sure about that: it just evolved naturally as it was used in portable devices predominantly. Same thing can be done with RISC-V-based designs, but obviously it will take a lot of time.
I suggest having a look into the actual pedigree of RISC-V, rather than making wild guesses.
It might have been born in academia, but from those drafts until the first ratified spec there's a good decade of high quality input from distinguished industry veterans.
