As one of those people, I can say the reason is for the C-level processing power with the approachable syntactic sugar. Out of all the languages gaining popularity for their ability to run natively (Rust, Go, D, etc), I've felt that D is the most natural continuation of C/C++, at least syntactically. I haven't touched the language in about a year, but I'm personally rooting for it.
And with D as Better C, (-betterC switch), it's easy to convert your C project to D, one file at a time, and not require the D runtime library (only the standard C library is required).
The original impetus for this was so I could incrementally convert the D compiler backend itself from "C with Classes" to D.
