No, really they don't.  Whats the primary purpose of a Visa or Mastercard?  Credit.  Second?  Convenience, instant transactions with about every vendor in the first world.  Third?  consumer protection

To the first, Bitcoin offers no credit.
To the second, Bitcoin offers delayed transactions, potentially to all vendors in the world. 
To the third, Bitcoin pointedly does not offer any consumer protection, theres zero redress from any problems like non-delivery, faulty merchandise etc.

I know someone will pipe in with fees here, but I don't pay fees.  Maybe you do in the US, but here in UK and in Europe the fees are hidden.
Chargebacks, another issue often raised, is a problem for the vendor too, not me as the user. 

Bitcoin is maybe have an affect on paypal and western union for peer-to-peer money transfer, but Mastercard and Visa are least affected.