For a long time D wasn't open source, didn't work very well on Windows, had a very limited standard library, and had poor IDE support. There's also a large divide in the community around garbage collection vs manual memory management.

I don't necessarily agree with the parent's point but D managed to fumble early on and never managed to catch up ever since. Around the time it got released (in the early 2000's) I was a C++ coder and I remember being very interested, only to immediately dismiss it as soon as I learned that it wasn't fully open source. I'm sure other devs didn't mind as much as I did but it definitely stunted growth early on. By the time they fixed this "issue" there was a lot of competition in that space and I never bothered looking back.