Control over the code that actually runs.

We already lose quite a bit of control with C (e.g. it reorders your code as it pleases) to gain portability across CPUs, otherwise we'd have to rewrite the code in several assembly languages.

If you consciously choose to give up even more control over the code that runs (because a compiler that targets C necessarily adds another layer of autogenerated code that you don't control) then it better be a wise tradeoff.