[1] https://github.com/ValveSoftware/source-sdk-2013 (originally released in 2004)
C wasn't much used in MS-DOS, as it was yet another systems language trying to gain the place of Assembly for high performance applications.
In some countries Pascal dialects (mostly TP compatible), Modula-2 reigned, while in others C and C++ were other contenders.
By the time Windows (written in C) became mature enough people started caring about it (3.x), C++ was already having its place via OWL (later VCL) on the Borland side, and Microsoft eventually came up with MFC.
However these were the days when C++ still didn't had a standard (which came in 1998), beyond the C++ARM book, so either you would stick with the compiler framework, or try to minimize language features for better portability.
Additionally on Windows everyone was learning it via Petzold's book, where he takes the approach C compiled with C++, not even "C with Classes".
Also although OWL and VCL were great OOP libraries with nice abstractions, MFC was pretty much a Win32 thin wrapper as its initial internal implementation (AFX) wasn't well received by internal MS employees as not being low level enough over Win32.
So there were lots of issues going on that lead to such cases.
Course back then STL (mostly now the standard library) was still sgi STL, and there was also RogueWave, both still fairly new and on the up.