There are two classes of payments - consumer and business.
This API is designed for business payments. Companies that process tens, if not hundreds of thousands of payments on a monthly basis. Think about the companies that sit behind businesses like Etsy or Uber - they need to take a lot of payments from customers and pay the supplier.
Many of those payment companies are financial institutions themselves who probably already have some kind of connection to programs like Visa.
This API is designed for business payments. Companies that process tens, if not hundreds of thousands of payments on a monthly basis. Think about the companies that sit behind businesses like Etsy or Uber - they need to take a lot of payments from customers and pay the supplier.
Many of those payment companies are financial institutions themselves who probably already have some kind of connection to programs like Visa.