This is the future, where many businesses no longer accept cash as payment. That means you are required to have a checking account to function in the economy. And if you're poor, that means at some point you're going to get bank-fucked.
Because having a checking account while poor doesn't just mean you have to be responsible and good at math -- you have to be perfect. Meticulous, flawless record keeping is the difference between surviving and having the bank seize your next paycheck.
Let's say you're running late for work and hurriedly stop to get gas, paying with a bank card. In your haste you forget to write the $55 down (gas being $4 a gallon, you know). So while you spent the last week until payday thinking you had $50 in your account to absorb minor purchases, you actually were $5 in the red.
So payday comes. You go to the bank to deposit your check, at which point the bank takes it, sticks it in their pocket and says, "Thank you very much! I'm buying myself a new pair of shoes with that shit!" They then inform you that your account was at -$200 at the moment you deposited your check.