Spot on, Kiltie.
An instrument approach is an essential to run commercial services, which then has to be maintained. That costs money.
Of course you could fly a 146 in there, no problem. Where are all the paying punters going to come from, though?
From the point of view of general terrain, weather, population etc, the area is not dissimilar to Eniskillen in N.Ireland where the airport (St. Angelo) used to be served by Jersey European (as it then was) by a Shed out of City of Derry (I believe) about twice a week in the tourist season. It has a small NDB but no published approach procedure. There simply is not the business to sustain a regular scheduled service.