I honestly really don't get why someone want to use js serverside, and I say that as someone who did create cool things with js client side and wants to know why I should spend time on this new cool stuff.
Edit: automatic upvotes for serious answers as long as I see them before going offline :-)
By using Node.js in a Web shop, you can eliminate one language.
Other benefits include re-use of client side code, async everywhere, and popularity.
To business decision makers, that looks like a better strategic decision - Now my web app devs can do server side! Obviously this is totally wrong, any decent developer can learn a new language/framework. The architectural concepts are totally different on server side, which is what HR should be hiring against. But hey, what do I know.
(Some other languages let you do that too)
Anyway, my point was that Node.js main core value was to let people script evented I/O over a lightweight runtime.
When Node came out, it was something new.
Java has a fairly rich NIO path that you can choose to take or not, and predates node.js. I believe the Tornado package for Python predates it as well.
Certainly, there's some advantage there...fewer surprises with 3rd party libraries that aren't non-blocking. But, there's downsides as well.
Because starting in the mid-late 90s, B- and C-rank universities began adopting Java over C++ or Pascal as a teaching language, producing a glut of graduates who knew Java. As IT needs grew because of the internet boom, companies built their systems with the language that the available programmers knew.
These days, more and more "teach kids to code" initiatives are starting with JavaScript because it's easy to get started with, existing in every browser known to man. With IT infrastructure in for another period of growth/change, especially in startups, it makes sense to build out in JavaScript because it's what incoming fresh programmers know.
It doesn't make much sense to me, but that is how they do in the corporate world.