I find this is a cultural thing. I have had it happen many times on flight into South America. When CP used to fly to EZE via Sao Paulo, lots of tour groups would board in Brazil to go to Buenos Aires, or vice versa. Once the plane had landed, clapping always broke out.

The only other times this has happened up in this part of the world was, as others have noted, when we've been through a patch of particularly turbulent weather [horrid flight through lightning storms on a CP 737 between YUL and YYZ] or had a similar harrowing incident [aborted landing at LGA].