The problem is there is now a big and growing gap between tier one regional airports and the rest, MME, BOH, CWL, BLK all have airports near by that are bigger and as airport operating companies do deals based on volume of passenger ( because their rental deals to the shops are based on the same volumes) it becomes more and more difficult to attract new business, once over say 5 years ago someone would have already stepped into WW shoes at CWL look what happened to MME when WW pulled out, Globespam had a quick flirt before going under.
The cost of providing security, immigration ATC fire, fuel farm and all that goes with it is colossal and a few charter flights a day don't cut it an extension to stay open for fire cover for an hour will cost at least a couple of grand, do the math it just doesn't add up.
The likes of Exeter 7 NWI will probably keep going and CWL but if your a spotter you'll need a big flask and a lot of patience if you want to see anything other than the odd flybe dash