Assembly is specific to the architecture, potentially in non-trivial ways. They either have to manually write support for each CPU architecture, or they need a

Assembly is specific to the architecture, potentially in non-trivial ways. They either have to manually write support for each CPU architecture, or they need a higher level abstraction language. C is basically that higher level abstraction language. The tooling also helps. C compilers do some pretty fancy optimizations. Again, they can either re-implement that inside their tool, or they can just output C and use the existing tools.