That's too bad. I guess OCaml is the non-mainstream language Facebook seems to be interested in.
One thing D and Nim are lacking is adoption by a large company, and I feel that's partly what's keeping them behind Go and Rust.
Andrei left fb in 2015 - probably due to their lack of commitment to D & his F stocks doing well.
Andrei works full time on the D language/D foundation. To my knowledge, his decision to leave Facebook had something to do with his family and his desire to work on D full time, not any problems with his employer.