People also forget that cash isn't free - you have to protect it (with a safe/locks/doors/armoured cars), count it, process it, watch for counterfeits, have change on hand, deposit it, and so on. And it's flammable.

Given a choice, there are lots of (big) businesses who would switch to debit/credit exclusively if that was an option, especially with the existence of branded credit cards. Home Depot would love nothing more than having all its customers using the HD credit card.