Comment by koreth1

Based on my previous experience on payment systems, there's a surprising amount of value in not having to maintain direct business relationships with the underlying payment providers. It is much, much easier to work with a company like Stripe than to work directly with Visa and MasterCard and the ACH network, and heaven help you if you're a small company that needs to do automated cross-border payments to a wide range of countries without a middleman. You'll probably also get much better support from a tech-focused company when an API starts freaking out.