it's all such a new operation...for the airport, the airlines, the train company, the taxis.....if only 20 pax get off the last flight and want a train, surely its not worthwhile laying on an 8-carriage train to Liverpool Street for them.....but if (eventually) there are several hundred people, i am sure minds will think differently.
For me, as a passenger on low cost carriers (not only) across the world, if there is no public transport, I make my own arrangements...no big deal and sometimes less stres.