Cost.
ARM and MIPS require licensing fees, and spinning your own new architecture will make your chips irrelevant. RISC-V doesn't charge you to use their instruction set, and it's already supported by developer tooling.
ARM and MIPS require licensing fees, and spinning your own new architecture will make your chips irrelevant. RISC-V doesn't charge you to use their instruction set, and it's already supported by developer tooling.