You have more complex programming languages like Rust/Swift that take comparably ages to compile compared with C due e.g. all the extra code that is generated a

You have more complex programming languages like Rust/Swift that take comparably ages to compile compared with C due e.g. all the extra code that is generated and that has to be optimized by LLVM (This one is quite slow AFAIK, too). C++ has its template instantiations with the same problem. Another aspect is how much more the compilers optimize, compared to the "early" days, modern compilers can often beat human programmers at optimizing assembly in a reasonable time and can do a lot more complex optimizations. In addition to that, you can couple it e.g. with linker optimizations like LTO/BOLT and you have even longer build times. I think another factor is the more and more dominant static linking model (Rust/Go/Swift). If I compile e.g. my program with the swift stdlib statically linked, it takes around 15 seconds for an incremental build, while using a dynamically linked stdlib it takes around 6 seconds. Sure it is just one benchmark, but static linking nearly everything won't have no impact.