When they switch to their iPhone mic, it literally sounds like the audio version of upgrading from 144p to 4K.
Apple may have already fixed this issue in newer firmware/models.
Fundamentally they are fighting an uphill battle with physics and they'll probably never win no matter how much tech is developed.
They have settled on multiple mics with noise suppression technology to try to isolate and amplify just the voice but it's still so much worse than the cheap approach of a single mic along a cable not too far from your mouth that it's laughable really.
In my opinion this is a case of tech for the sake of tech, it only exists to "fix" a perceived inconvenience (at least marketed) of having a cable but to do so it creates more inconveniences and actually degrades the experience/quality.
When you think about it, it's really marketing genius that they are able to sell them at all. Basically, selling worse audio quality (both mic and speaker) than what was available in the late 2000's at 2-3 times the price, all that to not have a cable.