For subtle technical reasons relating to the toolchain, it's not possible to use C++ for this platform.
Well, it is possible, but it would easily take four times the amount of time it would take to port the C++ code to C. So porting makes the most sense.
There are a few niche reasons. The entire GNOME/GTk stack benefits greatly in the realm of language interop from being C at its core. This is why it easily has bindings to every language ever.