I'm sure the first comment has it correct. US and AA miles are (or were in the case of US) easy to come by. Lots of people have a lot of them. And they are easy to redeem for premium cabins on a number of airlines. I've used mine for CX F to SE Asia the last couple of years (and will again this year). I'm sure that's the main reason.

I think there were a lot of *A reports for a while as well when it was easy to cash in relatively small amounts of UA miles for travel on premium airlines. And Aeroplan used to have such great, cheap F redemptions too. Now that they've devalued you see somewhat fewer *A reports.

It's great that this section is here though. Personally I am more interested in destinations than lounges, seats and menus/food. So whatever airline, doesn't matter.

My most recent travel was on paid tickets though AC to Japan which I wrote a report on and I am just back from a couple of weeks in Spain thanks to DL's cheap Z class fares to Europe. I'll write that report once I get the photos edited. (Credited the miles to AS)