It might be a case of that in those airports Ryanair hasn't be offered a good enough deal to expand compared to other airports across Europe. They have expanded quite a lot lately into Ukriane and Israel and Germany and the UK regional airports are up against that competition just as much as their local competition which for CWL would be BRS and BHX. I doubt APD helps many of the smaller UK airports in attracting routes from them when they can deploy the aircraft to places that don't have that.