real talk. who the fukk is walking around with a bunch of $100s when everything is debit card status (which they want you to do). if you need $ you get a few $20s from the ATM and keep it moving. you make a lot of "hood" transactions (haircut, bud, chinese food, etc) with paper money but how many of those are you doing with $100 bills?
Every time a merchant swipes a customers card through the machine for a purchase the merchant pays a fee (a percent of the transaction) to the service provider of the machine. It usually varies per service provider and whether or not you are using VISA, MasterCard or AMEX etc.. That's why some Gas stations charge a cheaper amount for cash gas purchases and higher for using a card. Some companies get PAID through those machines. Plus banks want you to use them for Overdraft fee's to hit the lower/middle class.
This is also the same for ATM machines for withdraws. There's a fee every time you take out money through that machine, which is why banks charges the customer for going outside of their "network" because it cost them money.
Now I admit that I still carry around my cards and everything for certain purchases and what not and I wouldn't recommend carrying around a bunch of hundreds anyway, but Cash is still king.
Small business's have them because that's all people carry nowadays. That's a possible sale you are losing if you told your customers "I can't take debit cards". The only bad part is that they don't want to have to make a trip to the bank everyday to deposit a whole sh*t load of cash. Bottom line if they had a choice, they much rather you pay in cash rather than a debit/credit card.