So looks like a decision being made at local or regional level. With Western regions more likely to add CWOP stations.
Here in Tucson, I was told ONE reason for adding CWOP data was to enable UofA / NWS-TUC to "record" RAINFALL in surrounding areas so as to better gauge ACTUAL rainfall excess (summer monsoon thunderstorms) or deficit (drought). Sorta like it's taken them this 'long' to discover that not ALL the rain falls ONLY at the airport...duh!
Also, CWOP has evolved from "dedicated" citizens collecting daily weather per strict "standards" in outlying areas for the Gobberment, to myriad home weather stations reporting 'local' weather with ±∞ (infinity) accuracies!