Its not just this industry, its most if not all. Everywhere around us, its a consumer-driven race the the bottom in terms of price whilst basic costs continue to rise. Like many airports, Luton is reliant on budget carriers who have massively increased traffic but also largely replaced more profitable carriers (to the airport) on domestic routes and dedicated package holiday providers.
The outcome is a basic terminal with extension after extension and customers who generally just want to be on and off their flight like they would use a bus so limited revenue for the airport (unless they can keep them waiting by the shop).
It shouldn't be a surprise that whilst the airport provides employment in a town desperate for the opportunities the airport does provide, those jobs are supported by relatively low income generating activity and so the pay is appropriately paid for what is mostly low-skilled work.