Because the credit companies are acting under the guise of the law. "I don't want to end business with you, but the law compels me to do this!" If you haven't broken the law, there's no way to appeal this decision they've made as they do not have a route for that.

That aside, the ability to pay a service is pretty much fundamental to its existence. Being able to at-will terminate any company you want, even ones that are provably innocent, with no way for them to so much as appeal against your decision is a worrying amount of power for a company to hold. I don't think that even the government can do something like that (at least not legally).