Interest isn't always found. Sometimes it's built. So long as you only have one potential customer it's actually smarter to change their minds with something you can push concurrently rather than wait for the next opportunity for a sale they might give you. Without changing someone's mind about buying the J-31 SAC would be facing a rather grim prospect for the next decade or so. Furthermore continuing the program on your own money can be seen as an investment on your next project because you're still improving your project management and understanding and mastery of the new technology, while keeping your workers sharp. Finally they may be looking to mature the design even if the PLAAF doesn't want it, because there's still a competition for the next naval fighter.
Number 1, I don't get all the animos against this beautiful airplane, it new, is fresh, somebody's paying for it, not you, so whats the problem, the J-20 is never going to be aboard ship, and the Navy wants/needs a fifth generation aircraft to meet their needs for Fleet Air Defense, this bird is NOT in competition with the J-20, and its got million dollar looks, so what not to like???