The GNU project can't go to the men's room without a thumbs up from Stallman, who is so disconnected from how real people do their computing that by his own statement he hasn't written any material amount of code in almost 20 years and can't even figure out how to update his own website, instead relying on volunteers to do so.

Stallman comes from the era when C was good enough, because computing was not a hostile environment like it is today.

GNU is never going to "rewrite it in rust" as long as he's living, and probably for several years afterwards.

In other words, it's a social problem not a technical one.