What they're banking in is that you switch and never notice when the promo period expires, just like most 0% financing offers, or gym memberships.

Our group didn't have all the data but did a rough analysis and concluded most people were spending the same or more than the default rate.

DLC bids out the default rate throughout the year so it might not be the absolute cheapest, it's pretty competitive.

I would save about $10/month when I would switch after the introductory rate.