They got the A321 as part of their package deal with Airbus. Why not get it? It is common to the A319, and the A320. Crew training can be eased as has a common type rating. Flight attendants can learn the A321 in a matter of seconds as it is just like the other Airbusses, just longer.
Why go for more 757s, when you have the airbus?
I L U V 7 6 7