A) A credit account is not the same thing as a checking account or credit union account
B) Plenty of people, even in the US, operate without any of these things. It's not fun, but it's absolutely possible.
After my company crashed, my wife divorced me and then I got cancer -- things were pretty grim on my credit-worthiness story. Net-net: I went without a bank-account for a few years and learned to live with pre-paid phones, money-orders, cashing checks at pawn-shops and pre-paid debit cards, and (for medical and other reasons - not able to drive. Good news: I saved on car insurance, gas and parking). All-in-all ... not a lot of fun (it's very expensive and time-consuming to be poor in America!).
But! As you say: it is do-able.
Monopolies aren't choices, and monopolies on essential services are coercive by definition.
It doesn't make much sense for borrowers, though. But since, by definition, the lenders have the money and the borrowers do not, the borrowers have no real ability to negotiate when lenders get together and do things like that.
But borrowers can vote just as much as lenders can, which is why such behavior is governed by law. So let's not pretend that borrowers somehow agreed to this system in any way. It was forced upon them, and the best they could do about it is pass laws to ensure that lenders at least had to be accurate when reporting, and had to respond reasonably to disputes. Since lenders can lobby and vote, too, borrowers were not able to mandate that the lenders would have much in the way of legal liability when they inevitably get lazy, screw up, and cause real damages to real people.
The law isn't fair; it's just the best compromise that adversarial parties with differing amounts of money, power, and motivation could reach a threshold level of agreement on. It just so happens that a savvy and motivated borrower can completely whitewash their own credit reports for the cost of a few stamps, and maybe some small claims suits, while an ignorant borrower, or one who lacks the time and energy to ride herd on the CRAs, can get completely screwed. It's a numbers game, and the lenders and CRAs can make more money from the latter category than they lose from the former.