I also said 'mindshare'.
Cs syntax can be awful. Similar symbols with different meanings. But, it was powerful, fast and simpler than some competitors.
Bash is frequently used today, for all sorts of things. Its even in production products, like git. However, even its creator thought it was a kludge.
There is no simple answer to language success, but a large group of people adopting and improving a language is probably going to be helpful.
d is not unpopular because of lack of corporate backing
d is unpopular because of poor project objectives and positioning and playing catch up with other languages rather than leading in any specific area
d needs a novel idea ... i guess they made bet on execution rather than innovation
more examples that debunk that corporate backing is what made rust or go ... are scala and clojure, scala being way more popular than d and clojure ... and neither have corporate backing
in conclusion, you dont really need corporate backing if you have a nicely designed language that have its own path