I think management plays a significant part here. Compare the three airports owned by AGS. Aberdeen, Glasgow and Southampton. All three have failed to truly embrace low cost airlines. All three are very conservative. All three are very "lazy" when it comes to attracting new airlines. While other airports and airport groups are out there banging on the doors of airline, AGS are sitting back waiting for the phone to ring.
Perhaps it stems from the BAA Heathrow days when airline were banging on their door. Sadly these three airports don't have that luxury. Whither AGS have realised that or not is unclear.