Echoes what I just said about Delta.
Someone once told me that flying long haul routes is considered the pinnacle for American cabin crew, and something of a prestige role (as well as being the best paid), thus the crew have to work their way up over the years and "earn" the right. Hence most of them have millions of miles under their belts, while the younger, newer crews work the domestic and commuter routes until they've earned their wings.
I guess they are also experienced in having to deal with constantly changing time zones regularly