I'd expect that most companies rely on one payment provider, at least in the early days. The cost of implementing, testing, etc. multiple providers is pretty high. I have only switched providers twice in the decade long life of my company, and only due to extreme pain from the previous one. It takes a lot to get me to sign on for the pain of a migration, and that's even more pronounced now that so much data ends up stored in your payment providers database; so, your customer data isn't even yours to migrate, anymore (AFAIK, I haven't crossed this bridge yet, but I guess I will one day, if Braintree, who I'm currently using, does something to make their service untenable for us).