Or they never carry a balance on their card

Responsibly using CC isn't about "relying on future income to pay off present debt". If you have 5k in the bank, don't spend more than that, and pay it off at the end of the month (or if you're paranoid like I was right out of school, pay it off every week)

Yeah originally I paid mine off every few days, means there's essentially zero risk

If you can't trust yourself, sure. But most people do have the ability to simply not spend more than they have in their bank account and then pay off in full even before they receive a statement. Even if you lost your job, you'd still be fine.