Hello Anders, that’s quite a technical response why that’s done and there’s a great answer in this forum: https://stackoverflow.com/questions/1041866/what-is-the-effect-of-extern-c-in-c

In summary: the Arduino IDE uses  C++, but the “FreeRTOS” and “Timers” library use C language. Using “extern “C” {” you can import/include those libraries in your code.

I hope that helps!