They might not be paying a big price today, but they do pay a price - their reputation is damaged and when other potential customers look at who to use, they give more consideration to alternatives.

How many businesses are they having to "shut down without explanation" that it doesn't scale? I understand if this was something like not responding to a wrong charge/refund etc for one customer. But here we are talking about shutting down someone's business without explanation. I do not think "scaling" is the problem here.

Also as someone else mentioned, as much as I love hating on Amazon, customer support is one place where they are absolutely outstanding. I have been able to reach out to their chat support and get issues resolved multiple times (refunds/item returns etc). If Amazon can scale it, then so can these payment processors.