Stateless web servers are one of those things which are ridiculously and easily parallelizable, you can scale a web server horizontally easily. The ROI of rewriting everything in another language as opposed to just adding more web servers would probably take years unless you’re running at a ridiculously large scale. For the cost of one developer’s fully allocated salary, you can throw a lot of hardware at performance issues with web apps.

I prefer statically typed languages, but performance isn’t one of them. Besides, how much processing is a typical web app doing?

Some example languages that come to mind here: Python, Ruby, JavaScript, Clojure, Groovy.

Go actually comes close here, even though it doesn't have a REPL and isn't very dynamic, because of its focus on minimizing cognitive overhead and getting the job done with minimal fuss.

Other languages carry a lot of community baggage. Java is one of the worst IMO...if you try to hire Java programmers, it's going to take a lot of effort and risk to find and reject applicants who've read too many design pattern books, are architecture astronauts, or come from an enterprise-y background. The signal-to-noise ratio is just really poor.

Now look at Ruby, its stack is gigantic and cumbersome.

I guess Go will try to resist that, but over time Go will become burdened with a huge stack of outmoded software.