Lack of training ?
Quite a mix of opinions above, I would hazard to guess that it is due to a lack of clear guide lines for the staff, there is probably a "system" for the GA sector but some of the staff have failed to understand or have not been told about the procedures and just decide to make up the "rules" as they go along and to avoid any chance of getting a bollocking from above they build in all sorts of extra "rules & restrictions".
Regonal airports could do with an attitude change to GA, too often they get a few loco airlines landing and see this as their only business, get the idea that they are some sort of intergalactic space port and reject GA as not being worth dealing with.
Airfield like Southend do need to build their business plan around commercial aviation, but having paid the bills with the revinue from the airlines the cost of fitting GA in should be minimal and yeald a higher % Proffit than the airlines. To be blunt if the airfield is paid for by the airlines GA should almost be money for nothing.
The other part of the issue is that a businessman using an airport is far more likely to bring money into the local economy that the loco passenger who arrives by train and gets on a flight, this is not such an issue for the airport as for the local politicians who should insist that the planing permission for airfield development includes GA friendly facility's to encourage easy access for business to the area.