I agree with you, it is just a call to reality to those "lets rewrite everything in language X", without consideration that there is more to it than just grammar and semantics.
Also there are plenty of domains where Java or C++ aren't even taken into consideration, in spite of decades of effort.
Just to cite Microsoft's recent security recommendation out of Blue Hat conference, regarding their own software, "use a mix of C#, Rust and constrained C++".