I am not sure thst this is necessarily so, as long as people can get from A to B. For example if I needed to go on business to New York, I could go HUY-AMS-JFK, MAN-FRA-JFK MAN-JFK as well as via LHR (via LBA or MAN). My company would not care which route I took as long as the price os ok, and I suspect a lot of firms take the same view. Eventually EU airspace will be facing restrictions so increasing airport capacity will provide little benefit.

Perhaps the thinking is let someone else take the the hit, especially with the climate change agreement which was agreed today, thereby UK plc gains the benefit whilst not having to outlay the capital expenditure. Sure the UK airline industries take a hit, but what percentage of the overall economy do they provide.

The UK has a proven track record of getting out of areas it can no longer compete in.