icc was discontinued FWIW. The replacement, icx, is AIUI just clang plus some proprietary plugins

I wonder how this relates to Intel's "One API", which extends a single C code base across the various CPU targets (such as the core ALU, base vector units, AVX-512, NPU) and Intel GPU accelerators.

Not the same thing, or perhaps an augmentation of Intel performance libraries (which required C++, I believe).

Sure, harmonizing all of this may have suggested that there were too many software teams. But device drivers don't write themselves, and without feedback from internal software developers, you can't validate your CPU designs.