If I’m a bank that’s has never heard of Joe Schmo (who’s asking for a credit card), how do I know how much credit to give and at what interest rate? Sure, I could give them a very low limit and high interest rate, and both would improve over time, but if my competitor next door can extend $5k at 15% by looking at Joe’s credit score, why would Joe come to me?
The reason credit scores exist is because there’s a market for that information, and the three companies took advantage of that. But because of that market, abuse had to be controlled, and Congress produced the FCRA. But even with that, there’s still the mess we have today.