Why does the stdlib implementation do so badly in the first place?

It is maybe the most simple web server implementation, similar to what you get from "python3 -m http.server"? What sense does it make to compare highly focused web server frameworks to languages most simple stdlib implementations, much apples vs oranges.. (thus also not getting why the proposal to compare with actual web frameworks for nim is that much downvoted?!)

Too much string copying iirc. It was written a while ago.

Hopefully it'll get updated/replaced some time, but there's plenty of faster 3rd party ones already.