The POSIX subsystem is a box checking exercise. The reason the box was there isn't satisfied but the box was checked and Microsoft hoped that's good enough. If you need "a Unix" and they give you NT and circle the stuff about POSIX you don't go "Oh, perfect" you ask them to fix the requirements document so that you can have an actual Unix next time.
replyWSL is Redmond going OK yeah, here you go, an actual Unix.
There was also SUA and Interix in the meantime, before WSL came to be.
replyThe point still stands, that POSIX checkbox was relevant enough for spending the money in engineers salary during Windows NT 3.51 development.