When you are living paycheck to paycheck, it's a lot harder to avoid going over. Then, even a small amount over can incur late fees, and if you can't pay it off for even a month, it results in a decent amount of interest.
So why is it necessary for these people to be using a credit card if they can't pay it back? Especially if they have an average income that is sufficient to cover their lifestyle. If they're going to be strictly worse off after engaging with a system, why are they engaging with it?
I lost you there a bit. Why can't debit card serve the same purpose?
It is easy to see how someone with no money would take out a loan via a credit card and be unable to pay it back at all. But if they can pay it back, then outside of very rare instances why can't they arrange their affairs so they have the equivalent amount of savings up front? Their income is at least equal to their expenses on average in the short term, they can't be using credits cards to cover long-term imbalances because the interest is too punishing. If their expenses are experiencing variances then there must be opportunities to put aside an emergency fund.
I don't see how the math checks out that they need and can afford a credit card if they can afford to pay some sort of "poor tax". If you can afford the extra cost of credit card interest, you can afford not to have one. Otherwise where are the bank's profits going to come from?