1) It's cheaper; ie, pennies to send a transaction of any size, not a fixed 2-3%. As someone noted above, merchants could pass those savings along.
But see, one of the reasons it is cheaper is because there is no insurance for the consumer. One of the reasons that Visa/Mastercard/Paypal charge transaction fees is because they offer insurance on transactions. That's worth something, and bitcoin currency doesn't offer that option for the most part. So it is nominally cheaper, but if you get ripped off enough, it may well effectively be more expensive.
2) Consumers do not expose ANY sensitive information when they execute a transaction, unlike every means of electronically sending fiat. As a consumer, I will not use a credit-card on sites that I don't have a good reason to already trust because I know that I'm handing them everything needed to steal a bunch of money from me if they're dishonest (or simply lax in their own IT security). Yes, there's recourse with credit-cards if fraud happens, but even in the best case scenario, it's a big pain to correct; and in the worst case, far more than my transaction amount can be lost.
3) Privacy (pseudo-anonymity), potentially.
As a consumer, I won't use bitcoin, period, on any site that doesn't have a great reputation (virtually none), because I have literally no recourse if I'm ripped off.
I've had people steal my credit card info (not the card itself) and proceed to run up $16,000 in charges. The credit card company just took care of that for me, at zero charge to me other than a bit of time. Until Bitcoin can offer that kind of protection, it will always be a niche currency at best. With Visa/Mastercard, I don't have to trust the site I'm on. I can spend money without thinking about it, because they've got my back. THAT is why they get their 2-3% from merchants, which the bitcoin community generally seems to fail to understand.
Happily, there are going to be well-backed companies that prove they deserve the kind of investment it will take to fund the creation of the insurance required for that trust, and they'll get that investment. Bitcoin isn't there yet though, and ultimately the different between bitcoin and Visa/Mastercard is probably going to be under 1%....but that's enough to build huge businesses off of given the size of the global retail market.