My opinion (with 20 years industry background working AA DFW Operations) is that pulling the Airbus from Hawaii is most likely a cost reduction for "fleet commonality".
Ask yourself ... what airlines operate narrow body (IE: A3xx series) Airbus aircraft to/from/within Hawaii ??
To the best of my knowledge, VX nee AS, is the ONLY such scheduled operator within the entire state.
I don't know how they have handled unshceduled maint problems while in Hawaii (with trained mechanics and/or a parts inventory). It's not like they can pick up the phone and call the local Airbus repair shop. However it was done, this had to cost VX serious $$$.
On a smaller scale, I thought the same when (a then AS owned) VX inaugurated service from SFO to KOA last December (I was on the inaugural flight
).
Why operate with an A320, when it will be the one and only A320 to the island each day. Wouldn't a 737 make more sense ?
Switching all Hawaii service to 737 has to be a cost savings for AS. While 737 service in Hawaii isn't too big, you can at least enter into agreement with UA to share the manpower/inventory/costs somewhat. And I'm sure the 737 shares a lot of components with the 757, also helping to ease the pain.