I would say they are trying to bundle a very profitable revolving line of credit with your charge card, in order to encourage you to use the charge card for major purchases which you might otherwise put on a MasterCard or VISA.
Agree with you, mia. But you'd think they would start offering this as a standard part of the card, rather than giving 5k/10k each time to entice someone. I find their approach a bit puzzling...