- I think the simple answer to nkurz's point on why don't all cards charge the maximum in interchange is - it's just market forces. It's not worth enough money to long-term piss off the bigger merchants (i.e. Amazon). When you have a 30% APR card non-rewards card, the 3% interchange is small beans. Also the acquiring bank would probably want a bigger piece of the pie if it were more widespread
- Credit Card economics is radically different across different countries (for all sorts of reasons). So for example, a third of card users in the US explicitly seek the rewards and another third have it for the various protections/security vs. debit cards. In the UK only 12% seek rewards, with the two biggest use cases being to spread costs of big transactions or to improve their credit score. (so for that reason it's sort of hard to have a global view of this problem)