Only the „interchange fee“ received by the issuer‘s bank is capped.Believe it or not. But in EU for example payment processing is caped at 0.3%
There are other fees and costs related to card acceptance and processing.
Still, even the smallest companies can accept cards online for less than 3%.
The EU interchange regulation is a great example though of EU regulation that benefits small businesses and consumers by decreasing costs of payment and increasing card acceptance.