That represents a misunderstanding of D. Unlike Go and Rust, which were built for one specific use case (Go for the work done at Google, and Rust for writing a browser), D is an all-around good general purpose programming language. If it did have a niche, it would be as a C replacement, and it is the best available tool for that.

Your comment also implies that D is not used. Download statistics, forum activity, and the existence of users suggests otherwise.