How about to skate great and show the International Committee that they may have made a questionable decision in skipping over him for the Olympic team? To show that his strong performance at Nationals wasn't a fluke? For pride?
It'd be a more satisfying end to his career than the disappointment of San Jose, wouldn't it?
And here's another reason to go to Taipei: both Ashley and Ross are alternates to the World team. I think there's a very good chance that Ashley, as first alternate, might get the call to go to Milan. It's very common for skaters not to go on to worlds after Olympics, suffering from exhaustion, injury or just plain burnout. Mirai especially might want to end her career on Olympic ice.
Ross, admittedly, has a much lower chance of being tapped for Worlds as the second alternate, but stranger things have happened!