I was flying Delta but I seriously don't do it for perks. Theae are people who will be serving us our food, literally coming to us when we ring a bell, and cleaning those nasty ass bathrooms. They deserve some appreciation. Also, I do it because that surprised smile when you hand over chocolates is worth a bazillion times more.
Those are the best reasons to do this! But after my last flight with American, where the gate agent gave me such a hard freakin time because my bag was a little too big to go into their metal box, I'm not inclined to kindness. She was definitely power-tripping that morning. But maybe that's just what she needed in that moment. (I took out my regulator and it went in fine - and on the way back the reg was in there and nobody hassled me about my carry-on).