Cash has high costs that likely make electronic forms of payment competitive.
You have
- Employees skimming the till;
- Theft insurance for a safe, the nightly amount in the safe
- Managers balancing the cash registers with change/safe
- Armored trucks picking up the money (2-3 men guarding the transfer)
- Banks processing the money
- Employee time and frustration ensuring they didn't come up short
tldr; It takes one armed robbery or employee malfeasance before ~2% fees seem very much worth it to reduce cash on hand.