C is a programming language made created in the 1970's by Dennis Ritchie who is also known for his work on Unix and his wonderful beards. C is used for pretty much everything ever; it has been used for games, operating systems, compilers, U.A.V on-board flight systems, adult toys, and it can even be used for making web apps. C even made an entire family of programming languages, which includes languages such as:
The short answer is because C gives you more control, the long answer is the following paragraph.
C overall has more support than any other language, with libraries like Sokol and Raylib being written in C. C alsois generally what your software will be running on. Built a Rust or Go app for Linux? MacOS? Windows? FreeBSD? Minix? Plan9? Your application still has to rely on the underlying system calls which are written in C. Even a program written in ASM and made to run on an operating system that isn't pure assembly will probably still have to use some C functions to do what it needs to do. Even if your programming a Rust app and building it on RedoxOS for a custom-built Rust-based microkernel then you will probably still have to support C if anyone wants to run anything that isn't written in Rust on your operating system.
You should also use it because it gives you more control than something like Rust or Go does and, if you want to be a real programmer, you should know what the computer is doing. Rust hides all of that under layers and layers of abstraction and "memory saftey", Go hides what the computer is doing through cryptic syntax, and C++ hides it through its general C++-ness. Meanwhile, C does not hide anything of what the computer does. You wanna write data directly to a memory address? Go ahead! The OS will not like it, but the compiler will have no problem with it. The compiler doesn't really have a problem with much, actually. It only really cares if you really screw something up.