I don’t think this is the only reason.

You could do this with Nim, Nim 2’s ARC model is compatible with c++’s RAII. Nim supports moves, destructors, copies, etc. see https://nim-lang.org/docs/destructors.html

You can import C++ classes, member functions, free functions, etc. easily with importcpp

importcpp for the code you are incrementally porting over. You could write a libclang script to do this for you. Exportcpp for what you any code that have been ported but have dependencies in C++ land.

My best guess is they want C++ compatibility and a new language due to preferences, more control over the compiler, etc. which are all valid reasons