i dont think you understand how bitcoin will actually work.
lets say you go to a cashcounter and want to pay via bitcoin. If its takes more than a few secs to confirm the transaction, it is not great for you or merchant. bitcoin fees have gone up the roof and transactions take a long time to confirm so visa will never be troubled by bitcoin.

next big reason is we use credit card to get a months credit for free ( if u pay on time). using bitcoin is like paying with a debit card as you need btc in. wallet to spend. we prefer to have merchant pay transaction fees to visa in return for free credit. unless fees are super low there is no incentive to accept btc