Maybe they need to build car parks close to Luton Parkway rather than at the airport, then force punters onto the DART.
Most travellers, I'd assume, will arrive LTN by car so if building car parks at the airport, then people will just not use the DART in the envisaged numbers.
Surely cheaper to have built a branch line from the main St.Pancras line into the airport. And yes, I know LTN is 500+ft above sea level.