As for Been There 'Because it costs money to keep an airfield open for large aircraft operations eg taxiways have to be repaired and kept FOD clear.' that rather begs a question as to how you think aircraft operate on airfields.
True, but if you reduce the number of operating surfaces you require the aircraft to operate on, you can reduce the maintenance costs. This might be why the majority of the taxiways are not cleared for large aircraft use at Wattisham and they use the ORPs to load/unload instead. That is what I was trying to explain.