Why are people writing critical infrastructure in [any language]?

In reality, the tools this article is referring to were written in javascript because they could be and it was the best tool for the job (according to the people who matter: the people who did the work).

If someone wants to rewrite them for speed and/or to chase the next shiny language, that's fine with me, but let's not kid ourselves that there was something wrong with using javascript in the first place.

Using the right abstractions (including the right number of abstractions) and the right data structures and algorithms is always going to trump the constants language choice can optimize.