Trouble is the CAA have made the ATC requirements and paperwork costs of setting up an RNAV app in the UK so outrageously expensive you will never see many here.
Considering the safety case and lack of infrastructure required by an airfield the cost should be minimal. All the required kit already in place, satellites up there and Avionics in the aircraft.
GPS overlay approaches on present NDB and VOR procedures could be published immediately and at minimal cost as was done in USA decades ago.
Small non ATC US airfield I visited had a GPS/LPV approach in place at each end of their runway in about 3 months at a cost of less than $20000.
And didn’t charge the usual UK £20/40 a go to use it.