Why bother? It's not like BTC is even that useful in retail. Let it first prove itself by conquering the international remittances market and e-commerce.
Why is it not useful in retail? I love the idea of not having to depend on a credit card company to buy simple, cheap items. If I can just scan a QR code and pay directly that sounds so much easier and convenient.
Volatility and it's kind of awkward having to pull out QR codes.
Also, in many places there are barely any cost savings as a lot of people do not even use credit cards but cheap chip and pin systems.