Newquay Airport ran fine, and profitably, back in the day when Brymon Airways had the lease of operating it in the day when it was, literally, a couple of oversized portakabins, a car park, a couple of baggage trolleys, a couple of clapped out fuel bowsers "Sweaty Betty" and "Fat Ann" and with everything else owned, operated, and provided for by the UK taxpayer, a.k.a. MoD (Air)
St. Mawgan/Newquay might be comparable to Machrihanish/Campbeltown, difference being that MoD (Air) still own and operate Machrihanish airfield whilst Campbeltown Airport remains pretty much as my description of Newquay Airport back in the day.
Perhaps because MoD (Air) couldn't find a sucker to take over and maintain/operate Machrihanish airfield whereas in Cornwall they found an entire county of suckers who, not necessarily by choice, agreed to taking over maintaining and operating St. Mawgan airfield!