The thing that's always special about C, it's basically the default goto programming language for calling from higher level code, most languages that support FFI do so by being able to communicate with C apis and having tools written around C. C also lacks more complex things like classes, it's much easier to build up a complex piece of software from C building blocks bound to your language. Think of like a struct that has a set of functions that operate on it. You can map that basically directly to a class definition in most higher level languages and then wrap up the c implementation details like memory management behind the scenes so you can produce a nice clean api in your chosen language to use.

This practice is fairly common in python when you're dealing with AI (I'm sure there's other examples, but this is the one that sticks out to me.) SDKs like TensorFlow are written in a lower level language (C++ I think for TF) and then FFI called from python, so you can end up with a function like initTensorFlow() and calling it is enough to bring TF online and ready to start processing other data.

And you may be thinking "Well, I can do all that in rust or go or <insert prefered language here>" and of course you can, ultimately it's all just a linker and compiler deciding where to put code and data in an executable, but C is the defacto standard and more tools from more languages are going to work well with it than say, rust or go. Which, now that I think about it, is probably why Rust supports defining a c api for your code, so it's easier to call from other platforms. Rust specifically tries to play nice with being embedded in existing projects because it makes it easier to adopt rust incrementally.

Just my $0.02