Payment costs asymptote around 2-3% for hidden reasons

Once you layer in customer support, consumer protection, fraud prevention, anti-money laundering controls, and credit, payment system costs seem to asymptote around 2-3% for hard-to-understand reasons, and much of this is remitted back to consumers as rewards, so it is unclear whether interchange should be counted as a transaction tax; evidence does not suggest the ~2% level is massively inefficient.