AFAIK, the POWER architecture consumes a lot of energy so it's not suited for mobile and/or embedded gadgets so it's not as appealing to the masses.
https://github.com/antonblanchard/microwatt
Although I guess it is less relevant now Western Digital has open sourced their RISC-V design as well.
Why is everyone so hyped up on RSIC-V and not something like POWER? When both are now fully open sourced.