> For example, it can be compiled on basically any platform that contains a CPU.

It will be pretty hard to find a platform which doesn't have at least a C99 compiler.

For instance even SDCC has uptodate C standard support (better than MSVC actually), and that covers most 8-bit CPUs all the way back to the 70's:

https://sdcc.sourceforge.net/

Also let's not forget that C99 is a quarter century old by now. That's about as old as K&R C was in 1999 ;)

> I'll use Zig or Rust or something.

I like Zig a lot (Rust not so much), but both Zig and Rust still have feature gaps compared to C99 which often makes me prefer C99 for day-to-day coding. Most importantly struct initalization both in Zig and Rust is very rudimentary compared to C99's designated init feature set - and somehow the authors of modern languages often don't see the benefits of having powerful data initialization features in the language. There are also lots of little paper cuts where both Zig and Rust balance convenience versus safety just a little too much away from convenience.