History and skills means squat, aggregate is king! Once that was exhausted
Hatfield was never dug up for aggregates. It was 'concreted over' with new housing and business parks. Radlett on the other hand, did go to aggregate production. In traffic terms it wasn't attracting enough away from the other airports to make money. The early 90's recession effectively killed it as did UK S.E. property prices and the requirement for housing space within the 'green belt'.
Also BAe weren't interested in paying Luton IIRC for ATC services in getting stuff in and out through controlled airspace. Luton did a lot of the co-ordination for their traffic in and out of controlled airspace. The relative proximity of Heathrow, Northolt, Luton, the Bovingdon arrival stack and Stansted all played their part in making it a concern for a viable future in terms of managing air traffic.