Lots of Legacy Software
Many companies cannot change, instantly all their code to C++ or similar.
Many companies cannot afford to change their code.
Many companies can afford to change their code, but don't care, or are "cheap".
Many companies are in the process of migrating, but, not yet finished.
Hidden Object Orientation
(Non Object Oriented) C source code designed as Object Oriented C source code, applications that are modeled with Object Orientation, and coded with "pure C", or tools that translate from "C++" or other O.O. progr. lang into C.
I heard that some video games are done that way. Some cross platforms tools also, and the GTK (GObject, GLibrary) visual interface library for the GNome Linux O.S. distributions.