Facebook managed to optimize mercurial (Python) to be faster than git (C) for their huge monorepo use case simply because Python made it so much easier to implement more efficient algorithms.

If you have some fairly simple function/task, then yeah, a C version will probably blow the Go version away almost all of the time. But that's not necessarily indicative of real-world performance of a full application.

And of course, there are other interests than "maximize performance" too, such as developer efficiency.