groundhand A good question and I think that it is simply down to what people have got used to. Many years ago, there was a Conductor on every bus to help the pax, reassure and give directions. Now there are hardly any. Train stations used to have porters and numerous other staff on the platform to do the same - not now.
So the airline world is simply the last of public transport to have lower fares and higher costs reach breaking point. Children that are just starting to travel by air now, will grow up knowing that the ONLY way to fly is to book and check-in online and then use a kiosk at the airport.