Because, if you look at the current trajectory of RISC-V micro-architectures: they will be competitive, so current hardware big tech will try hard to shut them down. If they are already at Zen3 performance... I run Zen2 and it's already beyond than enough (I miss AVX512 extensions though, hope we'll get often RVA cache line vector instructions on RISC-V).
Look at qualcomm already buying what seems to be a very good RISC-V microarchitecture, wonder what they will do to it (usually, they let it die slowly forcing their good engineers to work on something else).
The right way(TM) would be for ARM to "drop its ISA" and become a microarchitecture designer able to decode and run RISC-V ISA.
Intel and AMD should too. The world would be basically competing micro-archs all with high compatibility at machine code level.
And it seems nobody has been addressing the elephant in the room: x86 is an horrible ISA for a modern CPU, much more worse than RISC-V/ARM. It is only because AMD/Intel throw tons of money with tons of brains to make that horrible ISA performant AND because they are hogging the production capacity of the best silicon process.
There is zero wonders here.