Good point and I don't get that. Why AAL is at 54 today versus 33 one year ago is a total mystery to me. Labor costs have increased strongly... did I miss anything? Or did the stock go up because Buffett bought it.
I think it's mostly an expectations game, specifically related to three things:
(1) AA management has demonstrated what most analysts apparently view as a credible path to a moderating rate of cost growth by the end of this year as the company laps union raises and begins to realize post-merger efficiency/scale economies
(2) AA was the first airline to see unit revenue trends turn back positive once it got past all the negative YOY comps related to DAL, Brazil, etc.
(3) AA management has now articulated the timing for a peak in debt levels as capex starts to slow in the next 18 months due to, among other things, deferred widebody deliveries
In Delta's case, analysts were already more bullish about its long-term prospects and had more clarity on management's financial objectives and "targets" - since Delta management loves to talk about them - so I think there has been relatively less of a "bump" as Delta has delivered on its promises. Put differently - I think Wall St was pricing in a discount on AA stock because of uncertainty and/or lack of clarity on several of the items listed above, and as those things have started to become more certain and clear, the stock has appreciated.