Luton is an awful airport from a passenger point of view.... but it attracts airlines offering very cheap airfares. We may moan endlessly about how terrible the experience is when we actually fly.... but when we're sitting at home on the comfy sofa with our credit cards, we become cheapskates and decide we don't want to spend a penny more than we absolutely have to and somehow fool ourselves into thinking Luton will be better next time
Disclaimer - I've flown in or out of Luton over 150 times. You'd think by now I would have learned that Luton isn't going to magically become good next time...