Internal document at Meta written to explain why Meta only officially supported 3 languages at the time for server side development - Hack, C++ and Python. Rust is supported as well now, bringing the total number to 4 (https://engineering.fb.com/2022/07/27/developer-tools/progra...). The post explained why D was used at one point, but the use was phased out.

I no longer have access, but if a Meta employee is reading this, I'm referring to a post that called Alexandrescu a "whirlwind of energy" in terms of how he personally encouraged and enabled teams to adopt D for projects.