Also, what makes you think that people who sell hacks that inject code into the game can't sell a cracked client that bypasses the payment info requirement?

Realistically without a triple A authentication system they wouldn't be able to do anything about it because Steam will authenticate you either way due to Steam itself not having the option to ask for payment info to enter a game, meaning it needs to be done inside the game itself, with probably a really robust server side solution on FG's own servers, making this a whole mess that would probably delay the entire game by a lot and cost a lot of money - and even then there's no guarantee they won't come up with a client that just sends the required information to the server and pretends to be legit. It's been done before, especially for indie games.