Credit card txns, and other banking txns for that matter, will not go on the blockchain without first converting them to crypto. It's a public ledger, do you want your banking txns available for all to see? This doesn't even account for the massive amounts of fraud that would be involved since anybody can turn their phone into a credit card terminal if he/she wanted to.
The types of transactions where it would be worthwhile for a bank to convert and transmit via the blockchain, assuming a stable cryptocurrency, are very limited and would be cross-border transactions like tranfers associated with swift messages and trade finance.