Why can't we transpile C++ to D?

[Tejas via Digitalmars-d-learn]

Sorry, I'm rather ignorant when it comes to this, but why can't 
we use [pegged](https://github.com/PhilippeSigaud/Pegged) to 
transpile C++ code to D? Then we won't need a nogc compatible std 
library and so many other things could get easier, like getting 
legacy code to use Dlang. It might not be worth it for C+17 and 
beyond, but older codebases could benefit significantly, right?