One of the reason why I enjoy Japan is no tipping to the point that it is considered an insult to many service providers. Everyone prides themselves in providing the best service possible and making customers happy.
If someone can't do that in a service-oriented customer-facing job, then they should find another job. I hate tipping because there is already an expectation of good service when I purchase a product. If the company cannot pay their employees properly, then they should raise their prices accordingly to allow for fair wages. Airlines like AS have profit sharing schemes that gives employee a stake in their performance and success, which is one reason why I might be willing to pay a few extra bucks to fly with them over AA or UA on the same route.
Furthermore, I feel like many GAs might take this the wrong way, as others mentioned, a bribe and sense of superiority more than a gift of gratitude. They might even get in trouble for taking monetary gifts depending on company policy.