And that's precisely why D fails. D was marketed as nothing more than C++'s successor, right down to the naming choice. No one is looking for a better C++, therefore no one bothers with D.
Meanwhile, those who have to work with C++ keep their eyes in the C++ standardization process. Since D's inception, the C++ standardization committee already produced three standards which oddly enough do include stuff that is sought after by the C++ community.
It's great that C++ is catching up. It's almost got static if, except not because it introduces a new scope. Maybe next time...
The C++ programmers I know are attached to native code, but not exactly content with C++. Ethan Watson of Remedy Games (Quantum Break) said "we are an industry looking for salvation".
No doubt about it, many existing C++ users feel this way. I've read the same comment many times. Most programmers, however, are not C++ programmers, and they are not looking for a better C++. They are looking for the best programming language for their needs (which means in most cases they won't go anywhere near C++). Your comment about D being irrelevant doesn't make much sense.