That's largely because if you base a product on Arm or MIPS you have the choice of getting them to actively invest in and support you, or getting sued into oblivion by them.
THAT is why RISC-V is the most friendly ISA to innovation and where most future innovation will happen. Because innovation comes not only from internally inside Intel or Arm or MIPS (who have switched to RISC-V now anyway) but from a myriad of possible sources.
