Why the fuck is none using Intel MKL for AI or video codec despite being all matrix multiplication in disguise?

At least they admit that parts of it are optimized for Intel processors.

Back in late 90s or early 2000s there was a scandal where an Intel math library was optimized for only Intel chips. But benchmarks were using the library and saying AMD sucked because of these math routines.

Not sure what math libraries they use for benchmarks these days.

What do you mean? MKL is being used for AI, just not by default because CUDA is king still and MKL barely makes a difference on most consumer chips