There are many reasons, but I think the simplest is that using a language in house has a very real and non-trivial cost. Expertise, coding standards, library ve

There are many reasons, but I think the simplest is that using a language in house has a very real and non-trivial cost. Expertise, coding standards, library vetting, etc. 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.