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Certainly, when you acquire a credit card for travel, you want it to be versatile and convenient for any needs. Unfortunately, airlines want you to be loyal and only grant you rewards when you fly that one airline. Southwest wants you to fly Southwest and therefore gives small rewards on all other purchases. That's why unless you fly Southwest only, it's unprofitable to get a Southwest Rapid Rewards credit card - or other airlines cards in that case.
Fortunately, you have other options apart from getting a Southwest card. You can get a travel rewards credit card and earn miles on all airlines you fly. Such cards usually give you increased rewards on all travel purchases as well as a large sign-up bonus. Miles usually don't expire and are easy to redeem.