I'm not even talking about churning, though that can be a thing too.
I need to use something for purchases, and each method of payment has pros and cons. Even if using a credit card had a visible 2% additional cost, I'd use it on certain transactions. If I'm dealing with a vendor I might not trust to do a refund, a cc lets me do a chargeback. If I'm concerned about holding large amounts of cash, a cc lets me limit my risk exposure. If I don't have the cash currently, a cc give me an interest-free advance until the statement due date (between 20-40 days in the future).
We can certainly argue about whether those things are worth 1% or 3% or .02%, but they're worth something to consumers.