FlightPath:
In the US, it has been difficult for the airlines. Many of them spent quite a bit of money getting equipped, certified, and trained, only to find out they seldom get to use RNP. Just as with alot of the CATIII ILS, the airlines are letting the calibration, certs, and recency expire, to save money on costs.
Because they ended up placing too many RNP AR approaches were they are not needed nor particularly useful. Their purpose is where a significant terrain issue can only be resolved with RNP AR and, in a very few cases deconfliction and noise abatement.
If the FAA would get off the dime about letting non-astronauts fly RF legs, than ordinary RNAV IAPs with RF legs would provide the commonality ATC needs at very busy airports.
RNP AR has been terribily over "installed" in the U.S. and that continues because of programs and goals to be met by desk pilots.