I don't know...

.. Perhaps something about the same site being by the DOGE guys?

Seriously, posting to the same site owned by the Creator of DOGE, who is ethically responsible for mass death now and future deaths too.

Using the site supports him and his efforts.

My guess is that it's not complete or stable or qualified enough for them to publish it as a supported feature. Maybe the power draw is too high and it triggers thermal throttling too quickly, similar to early Intel AVX-512? Maybe they are still sorting out how to have each process choose SVE vs NEON mode, so libraries using the other one don't cause a fault? (Note that this seems limited to M4 and newer CPUs.)

I agree this is an important feature. I have very often wished that my Mac had wider vectors.

Besides Apple who is doing hpc on Apple silicon

Apple shipped their “Neural Engine” in lots of iPhones before publicizing or fully documenting it, could be part of their playbook.