I don't agree. UNIX was an extremely niche operating system until Linux won the data center, at that time both C and C++ were already extremely popular outside the UNIX world. C won because it was so easy to adapt to new hardware architectures (even GPU shading languages are just minimally extended flavours of C and C++).

Sorry, what? Most of data centers were running a UNIX operating system back in the day. What operating system do you think they were running?