I am sure that there are a lot merchants willing to accept Bitcoin as optional payment form, alongside the plenty of others they are working with, but most of them simply don't know Bitcoin, or they get distracted by the volatility. I am sure if they realize that they aren't exposed to the volatility if they make use of a payment processor such as BitPay, that they will definitely be open to accept it as payment form. It's a lack of understanding that plays an important role here. If I was a merchant that didn't know much about Bitcoin, then sure, the volatility will be a solid reason for me to not allow Bitcoin payments. But if I know we have third party payment processors that take care of everything, then heck, why not? I have nothing to lose, and the same goes up for others.
And how they take care of everything?
Could you explain it in layman terms how they help make payments in Bitcoin if I set my prices in, say, dollars? If Bitcoin price changes 50 dollars per coin every other day, of what help exactly could these payment processors be to me? Okay, I can set my prices in dollars and receive payment in dollars but why would I want let someone set prices for my goods in bitcoins? In that case, they would be my resellers not payment processors as I see it, though I don't think they are doing something like that at all