I mean, if you are being serious, there are tons of reasons to use the C API. I heavily use intrinsics in C++ templates. Clever use of templates allows me to write a function once which can compile to SSE/AVX/AVX-512 and different data types (float/double) and different arch (x86/x64). In most situations this will be faster than assembly since I can inline everything wherever I want. When the need arises I will drop down to assembly to try to get any last perf gains, but otherwise I found that clang/icc/msvc are pretty good at generating assembly.