C is to modern languages like Roman civilization is to Western culture today. An essential underpinning of how we think about things, admirable in many ways, but with horrible downsides, and not to be emulated. There are still some Latin speakers, but they are confined to a niche where nothing else but Latin feels right for them. But everyone else has moved on.
1. there's a lot of literature on the fundamentals that use C/C++ in examples, and the Linux kernel is still primarily written in C
2. as Dennis Ritchie said, "C is quirky, flawed, and an enormous success." I believe that's the Lindy effect at work
3. learning C can open up a deeper understanding of how things work
Once you know C... You appreciate programming in any other language.
A C Programmer