See, like the old 747SR, the 787-3 was primarily developed for the Japanese market. Both ANA and Japan Air Lines placed orders for the -3 so they could fly them within Japan with a bunch of passengers. The highly congested airports of Japan combined with high demand made for an ideal market. But things change. Tokyo has been getting more runway capacity, so the need for high density airplanes will be dropping somewhat.
As the 787 project continues to see delays, the -3 kept getting pushed further and further out so that also makes it a tougher sell. JAL had walked away from the -3 before, and now, ANA has followed suit. Boeing should be thrilled.
The 787-3 was just a distraction for Boeing. It was never going to be a big seller, and in fact, I would have been surprised to see anyone outside of JAL and ANA order one. Boeing had already shifted resources away from the -3, but it would have had to devote more time and effort to it at some point. Now it can just forget about that dog and move on to what matters.
The 787-8 needs the most resource right now, but the 787-9 isn't far down the line. And then there's the potential issue of the 787-10. That airplane hasn't been announced yet, but with Airbus winning some high profile orders based on the A350-1000, Boeing is going to have to take another hard look at this. At least now they can do so without having to worry about the -3.