For example, Erlang is great when you need to do lots of concurrent operations with guarantees about safety and uptime, but not really what I'd write a CSV parsing program or email client in.
C is very easy to link against on almost every platform and language, so basic libraries are often written in C.
Javascript (in the form of nodejs) is great for writing simple web servers because most of its standard library is asynchronous by default. Compare Python (with Tornado or similar) where lots of popular libraries cannot easily be used in an event loop.
I could go on forever, and you might disagree with me about a particular details, but the general point stands. If you took an expert Erlang programmer and gave her a day to write a spreadsheet application, you'd get a worse result than the same day spent by a C# programmer.