If I were to guess: AVX512 vector and mask register take space on the die, which is a finite resource and could be allocated to other things. Moreover, power

If I were to guess: AVX512 vector and mask register take space on the die, which is a finite resource and could be allocated to other things. Moreover, power consumption may have also been a challenge, as seen in the early Intel implementations of AVX512 (especially Skylake-X). And while AVX512 can improve single-threaded performance, that's only for applications that make use of it. And up until recently, that number was extremely limited.