Nim punts too many things to random GitHub libraries. Tagged unions with exhaustiveness checks for something like pattern matching on them is the responsibility of some random person in the Nim community, for example, which is a step too far, IMO.

I think what it comes down to is that the creator/BDFL of Nim has an eclectic set of things that he simply doesn't care about and will never add to the language even though they are basically table stakes nowadays.