why does virtually every successful business take credit and debit cards?

An average of 35% more sales than those who do not accept them*

More Customers, as you may or may not know many people literally live off of credit cards, if you take cash only this large segment of customers will not be yours

Easier, there is no need to give change, no need to deposit cash in the bank (funds are automatically deposited).  

​Less Theft, the risk of employees or customers stealing cash or losing cash is removed. 

Safety : Funds are automatically deposited into your bank or credit union account with no risk of them getting stolen

Business Funding : its often easier to get loans for businesses with good accounting who take credit/debit cards and have good accounting over those that are "cash only".

Higher Value for your company : ts often easier to sell companies easier and for higher amounts  who take credit/debit cards and have good accounting over those that are "cash only".