First, Android Pay has NOTHING to do with Isis/Softcard. That was a failed venture from Verizon, Sprint, and AT&T. Android Pay is almost identical to the contactless payment part of Wallet. It's even better, since you don't have to even open the app. Just unlock your phone and hover it over reader. Done.

As for the Aadvantage Card, I got confirmation from Citi that American Airlines hasn't approved it yet. I haven't gotten an answer from AA as to why they support Apple Pay but not Android Pay. It could be that it's making its way through the approval process, they have an exclusive deal with Apple, or no one has asked them to support it yet. But it's not Google's or Citi's fault for now...