The problem is that while D is absolutely better than C or C++, it is only 10-20% better, not a step function improvement like Rust is. A language that's only 10-20% better just cannot get enough traction against a deeply entrenched language.
I mean... Modules versus header files, 13 times faster compilation, introspection, unittest, etc. etc. etc. Okay, it's more like death by a thousand cuts but once you produce with D, you can't even touch C++ anymore. I am in that state...