I don't know, but I have some ideas. I've blogged about bitcoin many times, including on our company blog here:

http://www.foxycart.com/blog/why-does-foxycart-support-bitcoin
http://www.foxycart.com/blog/why-shouldnt-you-accept-bitcoin
http://www.foxycart.com/blog/integrating-foxycart-coinbase

We saw very little interest. I think many merchants only do what their customers demand for them to do. It makes no sense to add a payment method your customers aren't demanding. The number of sales they are potentially losing by not offering it is near zero and they don't think they'll get enough new customers with it to justify the perceived risks.

What are those risks?

Well, many just hear the mainstream media headlines when it comes to bitcoin and those are usually filled with scare stories of theft, drug dealing, child trafficking, hackers, and those "evil anarchists." Yes, I know, it's sad what passes for "news" and "journalism" these days. Few, if any, listen to experts like Andreas Antonopoulos or do real research to figure out how little bitcoin is used for crime compared to cash. So the risks include:

1. Having your brand associated with something scary.
2. Not understanding the complexities of how coinbase/bitpay convert to USD for you.
3. No chargebacks
4. Adding confusing steps to checkout which might cause cart abandonment ("Hey, what's this bitcoin thing? I'm going to go research that...").

Ultimately though, I think it's a chicken/egg problem. If enough customers demand a bitcoin/SBD payment system, merchants will add them. When they do, we'll be there to help.

Moral of the story: Every time you buy something, ask the merchant if you can pay with SBD or bitcoin. If they look at you funny, explain it quickly and succinctly and move on.