Luton is no Heathrow. Companies are not going to relocate to Luton so their employees can fly to Ibiza for a business trip
Sorry to be negative about Luton but that might be the case - but the Oxford Cambridge Arc will provide Luton with catchment. Stansted perhaps will take at the eastern end but the government wants many new homes between Bedford and Milton Keynes.
However on the other hand one could argue that with climate change air travel may have peaked and ask whether London needs more capacity.