Interest Free Credit Cards On Purchases

How to profit on bank credit cards?
Many banks are issuing credit cards for free. How these profit banks giving Free Credit Cards. If we buy something on credit card, the bank has to pay money to the sellers and pay only after say, 45 days. The bank loses interest in the 45 days. So how does it work?
The bank charges the seller between 1 and 3% of purchase to accept your card. So if you buy something for $ 100 at Walmart with your Visa, Visa Walmart for $ 99 and keeps the other $ 1 as a benefit. Same with debit cards, but it is a% smaller.
Money Management & Personal Finance : What Is APR for Credit Cards?