This isn't always a useful way to look at it. For a startup or small team especially, any time spent learning a new programming language is time spent not working on the core product. Yes, you might be better off in the long run using a more foreign programming language, but then again the business might not survive that long if you aren't actually building anything.

Also, it's easy to learn a language's syntax over a weekend, but it generally takes a lot longer to start being productive and writing idiomatic code in a new language, especially if you're also learning a new platform. That's time that you or your team may not have.