Speaking as the author of that change, and also as a long time user of C++ (in other projects), I hear ya! But I don't have the power to make PostgreSQL switch to C++. Years ago, std::sort() vs qsort() was almost a standard example of how C++ can be faster than C.

src/lib/sort_template.h is an example of a pseudo template function, but we also have at least one pseudo template container in src/lib/simplehash.h.

And if you want to see some "policy based design" (C++ community term) in PostgreSQL C code, check out src/backend/exec/nodeHashjoin.c. It uses forced inlining to "instantiate" two different versions of the hash join executor code, one with parallelism and one without, so that we don't have all the "am I in parallel mode?" branching/code size in the generated code.