Blackpool is in an almost unique position amongst British airports in that it is built very close to a residential area with unrestricted on street parking.
All airports these days need to supplement their income by car parking charges, but in Blackpool this income is much harder to obtain.
I well remember in the pre-ADF days, the arrival of the Ryanair flight would be followed by dozens of passengers walking out of the airport entrance with their wheeled suitcases down the local streets to their cars.
I imagine that Ryanair were offered very cheap landing fees on the assumption that there would be a reasonable supplement from car parking.
When there was a shortfall on anticipated income, the ADF was devised.