It is still being used. That is the simple answer. An even older language C is used in programming IoT devices such as Arduino, Photon and similar boards. So, if you understand C++ a more complex version of C, you can program IoT chips. Also, the principles of programming are the same in all languages. Once, you learn one learning another is a process of learning the syntax and vocabulary. Much like learning a foreign language, but much simpler.
Believe it or not there are programs out there running in C++ and even older languages and at some point somebody may someday have to fix them or figure out how to convert them to a newer language.