Question: Why shouldn't you?
Simple fact: Most software today is still written in C and C++. I use Gentoo Linux at home, and nearly all software I install uses gcc to compile C/C++ sources. There is some Python and Perl mixed in and I use Java for things like WebStorm, but without C/C++, my computer would not work. Don't forget about other every-day appliances, like smart devices and IoT. If you want to program for embedded, C is the way to go (though work is done to get an even better experience out of Rust).
Another simple fact: Our big operating systems (and kernels) today rely mainly on C/C++. Windows, macOS, Linux, BSD. There are a few newcomers, like NodeOS and Redox, which do not use C/C++, and I am quite excited about seeing them grow. However, if you want to grasp how your platform works at a low level (or even extend it), you will need C/C++ most of the time.
While the Hashnode community might be quite opinionated with all the web devs, outside of web development, C and C++ have a very important role. As a result, if you plan to make it as a developer on a system or application level, you should learn C/C++. It will help you write very performant and low-level code when it really matters and better understand lots of APIs (for example DirectX, OpenGL, Vulkan in the graphics corner). Also, it will definitely further your horizons!
So, even in 2017, with lots of JS everywhere and new languages which try to replace C and C++, these languages are still very very common and important. I would even say, they will stay relevant for years to come, if not decades!