.......but only recently on low cost and never on charter
What you have to remember is that most of the pax on low-cost and charter airlines are from a background that would have been doing "Wallace Arnold" coach tours a few years ago until air fares came within reach.
The clapping thing is a follow-on from the days when a cap would be passed around collecting tips for the driver!
As Tight Slot says, it
is rather nice, rather polite and rather British!