Because the system runs on debt. If you live within your means and don't borrow money, when you decide to borrow money for a big purchase, like a house or car, you are treated as a higher risk than someone with already crippling debt.
Want a job? They're gonna check your credit score. Want an apartment? They're gonna check your credit score. It's what matters now.
Hell, I wanted to upgrade my internet, so I went to Comcast and signed up for their internet. $60 a month, electronic withdrawals, no problem. Then they told me I could upgrade my phone service at no extra cost. They would even upgrade my phone to the newest model. All at no extra cost.
I've already signed a contract to pay them this money every month. But the phone, which was no extra cost, remember, I couldn't get because my credit score wasn't good enough. Never mind that I have enough money to buy a dozen phones in my bank, I can't get the phone because I haven't put myself in debt. Never mind that I could buy a phone, or just use the one I have now, I can't do it because of my credit score.
Oh, and the fact I have had the same plan for over 20 years with the same carrier and never missed a payment, that's irrelevant. But did I buy a ton of useless **** with my credit card? Very important.
Banks are like Vegas. They're gonna come out on top no matter what. And like Vegas, they get to change the rules to suit them.